Probability

NCERT Class 12 Mathematics Chapter 7: Probability (Pages 406–438)

Summary of Probability

Playing 00:00 / 00:00

Probability Summary

In this chapter, students will delve into the fascinating world of probability, a branch of mathematics that helps to quantify uncertainty. Probability is not just a method of guessing, it's an analytical tool that can help us understand and predict outcomes in a wide range of situations, from flipping coins to complex statistical models. To start, we will recall some foundational ideas of probability, including basic definitions and the concept of the sample space. A key focus will be on conditional probability, which studies the probability of an event occurring given that another event has already occurred. For instance, if we know that it is raining today, how does that change the probability of us attending an outdoor event? Such considerations are vital as they often appear in real-life scenarios. We will learn how to calculate conditional probabilities using the formula P(E|F) = P(E ∩ F) / P(F), assuming that P(F) is greater than zero. An important aspect of this chapter is the exploration of the properties of conditional probability. The chapter will also introduce Bayes' theorem, which helps to invert conditional probabilities, allowing us to calculate the likelihood of a hypothesis given observable evidence. For example, if we know the probability of a disease and the probability of a positive test result, how can we find out the probability of having the disease given a positive test? Bayes' theorem is incredibly useful in fields such as medicine, finance, and data science. Moreover, students will encounter the multiplication rule of probability, which allows us to find the probability of the simultaneous occurrence of two or more events. This rule becomes particularly handy when dealing with independent events, where the occurrence of one event does not influence the occurrence of another. For independent events, the multiplication rule states that P(E ∩ F) = P(E) × P(F). Toward the end of the chapter, we will explore the concept of random variables and their probability distributions. A random variable is a variable whose values are determined by the outcomes of a random phenomenon. We will discuss how these random variables can be discrete or continuous and how to derive their probabilities. In conclusion, this chapter lays the groundwork for more advanced topics in statistics and helps students develop a solid understanding of how to approach problems involving uncertainty. By the end of the chapter, students will be equipped to apply probability concepts to real-world situations, using mathematical reasoning to interpret data and make informed decisions.

Probability learning objectives

  • In this chapter, students will delve into the fascinating world of probability, a branch of mathematics that helps to quantify uncertainty.
  • Probability is not just a method of guessing, it's an analytical tool that can help us understand and predict outcomes in a wide range of situations, from flipping coins to complex statistical models.
  • To start, we will recall some foundational ideas of probability, including basic definitions and the concept of the sample space.
  • A key focus will be on conditional probability, which studies the probability of an event occurring given that another event has already occurred.

Probability key concepts

  • In this chapter on Probability from Mathematics Part - II, students explore the theory of probability as a quantitative measure of uncertainty.
  • The chapter introduces various topics, including conditional probability, which assesses how the likelihood of an event changes based on another event's occurrence.
  • It also discusses Bayes' theorem, the multiplication theorem on probability, and the independence of events, providing real-life applications and examples.
  • Students will learn to apply these concepts to solve problems involving discrete sample spaces and probability distributions, including the binomial distribution.
  • This chapter reinforces the relationship between probability theory and logical reasoning, highlighting its significance in mathematical frameworks.

Important topics in Probability

  1. 1.This chapter on Probability covers essential concepts including conditional probability, Bayes' theorem, and the multiplication rule.
  2. 2.It provides a foundational understanding crucial for advanced mathematical studies.
  3. 3.In this chapter, students will delve into the fascinating world of probability, a branch of mathematics that helps to quantify uncertainty.
  4. 4.Probability is not just a method of guessing, it's an analytical tool that can help us understand and predict outcomes in a wide range of situations, from flipping coins to complex statistical models.
  5. 5.To start, we will recall some foundational ideas of probability, including basic definitions and the concept of the sample space.
  6. 6.A key focus will be on conditional probability, which studies the probability of an event occurring given that another event has already occurred.

Probability syllabus breakdown

In this chapter on Probability from Mathematics Part - II, students explore the theory of probability as a quantitative measure of uncertainty. The chapter introduces various topics, including conditional probability, which assesses how the likelihood of an event changes based on another event's occurrence. It also discusses Bayes' theorem, the multiplication theorem on probability, and the independence of events, providing real-life applications and examples. Students will learn to apply these concepts to solve problems involving discrete sample spaces and probability distributions, including the binomial distribution. This chapter reinforces the relationship between probability theory and logical reasoning, highlighting its significance in mathematical frameworks.

Probability Revision Guide

Revise the most important ideas from Probability.

Key Points

1

Probability Definition

Probability quantifies uncertainty, expressed as P(E) = number of favorable outcomes / total outcomes.

2

Sample Space (S)

S defines all possible outcomes of an experiment. Example with coin toss: S = {H, T}.

3

Event Types

Events are subsets of S. A simple event contains one outcome; a compound event includes multiple.

4

Complementary Events

The complement of event E, denoted E', is defined as E' = S - E. P(E') = 1 - P(E).

5

Conditional Probability

P(E|F) = P(E ∩ F) / P(F) quantifies the probability of E given F has occurred, provided P(F) ≠ 0.

6

Multiplication Rule

P(E ∩ F) = P(E) * P(F|E) calculates the joint probability of E and F occurring together.

7

Independent Events

Events E and F are independent if P(E|F) = P(E). This means the occurrence of one does not affect the other.

8

Addition Rule

P(A ∪ B) = P(A) + P(B) - P(A ∩ B) calculates the probability of either A or B occurring.

9

Bayes' Theorem

Used for finding reverse probabilities: P(Ei|A) = [P(Ei) * P(A|Ei)] / P(A) for partition events Ei.

10

Law of Total Probability

P(A) = Σ [P(Ei) * P(A|Ei)] for a partition {Ei} of the sample space S.

11

Random Variable

A random variable is a function that assigns a number to each outcome in a sample space. Example: X = number of heads.

12

Probability Distribution

Describes the likelihood of all possible values of a random variable, including discrete and continuous types.

13

Binomial Distribution

Describes the number of successes in n independent Bernoulli trials, with P(X=k) = (n choose k) * (p^k) * (1-p)^(n-k).

14

Expected Value (Mean)

E(X) = Σ [x * P(X=x)] gives the average outcome for discrete random variables.

15

Variance

Defines the spread of a random variable: Var(X) = E(X²) - [E(X)]².

16

Common Misconceptions

Not all events are independent; disjoint events cannot happen at the same time.

17

Frequent Applications

Probability principles apply in diverse fields, including finance, insurance, and data science for risk assessment.

18

Expectation in Real Life

Used in making decisions under uncertainty, e.g., predicting sales or project outcomes.

19

Simulation in Probability

Monte Carlo methods help visualize probability through random sampling, useful in complex scenarios.

20

Practice Problems

Solve numerous problems to master concepts, particularly conditional probabilities and distributions.

21

Summary of Key Formulas

Keep handy: P(A ∩ B) = P(A)P(B|A), P(A|B) = P(A ∩ B)/P(B), and E(X) and Var(X) definitions.

Probability Questions & Answers

Work through important questions and exam-style prompts for Probability.

Show all 73 questions
Q9

What is the probability of NOT rolling a number greater than 3 on a fair die?

Single Answer MCQ
Q-00078446
View explanation
Q10

In a random experiment, if P(A) = 0.3 and P(B) = 0.6, what is P(A or B) if A and B are independent?

Single Answer MCQ
Q-00078447
View explanation
Q11

If a card is drawn from a deck, what is the probability that it is a face card?

Single Answer MCQ
Q-00078448
View explanation
Q12

Given the probabilities P(A) = 0.4, P(B) = 0.5, and P(A ∩ B) = 0.1, what is P(A|B)?

Single Answer MCQ
Q-00078449
View explanation
Q13

In a bag containing 5 white and 5 black balls, what is the probability of drawing one white and one black ball in succession without replacement?

Single Answer MCQ
Q-00078450
View explanation
Q14

What is the probability of getting a sum of 8 when rolling two six-sided dice?

Single Answer MCQ
Q-00078451
View explanation
Q15

If a box contains 4 red, 3 blue, and 2 green balls, what is the probability of drawing a red ball first and then a blue ball second, replacing the first?

Single Answer MCQ
Q-00078452
View explanation
Q16

What does the notation P(E ∩ F) represent?

Single Answer MCQ
Q-00078469
View explanation
Q17

If P(E) = 0.5 and P(F|E) = 0.2, what is P(E ∩ F)?

Single Answer MCQ
Q-00078470
View explanation
Q18

In an experiment, if A and B are independent events, which equation holds true?

Single Answer MCQ
Q-00078471
View explanation
Q19

What is the probability of drawing two black balls from an urn containing 10 black and 5 white balls without replacement?

Single Answer MCQ
Q-00078472
View explanation
Q20

If P(A) = 0.4 and P(B) = 0.5, what is P(A ∩ B) when A and B are independent?

Single Answer MCQ
Q-00078473
View explanation
Q21

In a roll of a die twice, what is the probability that both rolls are even numbers?

Single Answer MCQ
Q-00078474
View explanation
Q22

Three cards are drawn from a pack of 52 cards. What is the probability that the first two are kings and the third is an ace?

Single Answer MCQ
Q-00078475
View explanation
Q23

If P(E) = 0.3 and P(F) = 0.6, what is P(E ∩ F) when events E and F are not independent?

Single Answer MCQ
Q-00078476
View explanation
Q24

For two events E and F, if P(E) = 0.1 and P(E ∪ F) = 0.6, what must be true about P(F)?

Single Answer MCQ
Q-00078477
View explanation
Q25

What is the probability of drawing two aces consecutively from a standard deck without replacement?

Single Answer MCQ
Q-00078478
View explanation
Q26

If two events are mutually exclusive, which is true about their intersection?

Single Answer MCQ
Q-00078479
View explanation
Q27

What does the outcome P(E ∩ F) imply if both events have zero probability?

Single Answer MCQ
Q-00078480
View explanation
Q28

When extending the multiplication rule to three events, what is the correct form?

Single Answer MCQ
Q-00078481
View explanation
Q29

What is the formula for calculating conditional probability P(E|F)?

Single Answer MCQ
Q-00078482
View explanation
Q30

If P(A) = 0.3 and P(B) = 0.5, what is P(A|B) if A and B are independent?

Single Answer MCQ
Q-00078483
View explanation
Q31

In a card game, what is the probability of drawing a heart given that a red card has been drawn?

Single Answer MCQ
Q-00078484
View explanation
Q32

What is the conditional probability of event A given event B when P(A ∩ B) = 0.1 and P(B) = 0.25?

Single Answer MCQ
Q-00078485
View explanation
Q33

If P(A) = 0.6 and P(B|A) = 0.4, what is P(A ∩ B)?

Single Answer MCQ
Q-00078486
View explanation
Q34

What is P(A ∪ B | C) if P(A|C) = 0.5, P(B|C) = 0.2, and P(A ∩ B|C) = 0.1?

Single Answer MCQ
Q-00078487
View explanation
Q35

If two events are independent, what can we say about P(A ∩ B)?

Single Answer MCQ
Q-00078488
View explanation
Q36

In a family with two children, what is the conditional probability both are girls given that at least one is a girl?

Single Answer MCQ
Q-00078489
View explanation
Q37

What is the probability of getting a sum of 4 when rolling two dice?

Single Answer MCQ
Q-00078490
View explanation
Q38

If a die is rolled, what is the conditional probability of rolling a 1 given that an odd number has been rolled?

Single Answer MCQ
Q-00078491
View explanation
Q39

What is the conditional probability that event A occurs given that event B occurs, if P(A) = 0.3, P(B) = 0.6, and P(A ∩ B) = 0.2?

Single Answer MCQ
Q-00078492
View explanation
Q40

What is the conditional probability of obtaining a 3 on a die given that the roll is odd?

Single Answer MCQ
Q-00078493
View explanation
Q41

Two coins are tossed, what is the conditional probability of getting at least one head given that at least one tail is obtained?

Single Answer MCQ
Q-00078494
View explanation
Q42

If the probability of event A occurring is 0.4 and the probability of event A given event B is 0.5, what can be deduced about events A and B?

Single Answer MCQ
Q-00078495
View explanation
Q43

If P(A) = 0.8 and P(A|B) = 0.6, what is P(B) if A and B are independent?

Single Answer MCQ
Q-00078496
View explanation
Q44

If a test for a disease is 90% accurate, what is the probability that a person has the disease if they test positive, given that the overall disease prevalence is 0.1%?

Single Answer MCQ
Q-00078497
View explanation
Q45

If two events A and B are independent, which of the following represents the probability of both events occurring?

Single Answer MCQ
Q-00078498
View explanation
Q46

A factory produces three types of bolts with different rates of defects. If a bolt is found to be defective, what is the probability it was made by machine B?

Single Answer MCQ
Q-00078499
View explanation
Q47

A fair coin and an unbiased die are tossed. Let A be the event ‘head appears on the coin’ and B be the event ‘3 on the die’. Are A and B independent?

Single Answer MCQ
Q-00078500
View explanation
Q48

A doctor arrives late to an appointment. If the transport methods are varied, what is the probability he came by train?

Single Answer MCQ
Q-00078501
View explanation
Q49

If P(A) = 0.4 and P(B) = 0.5 for independent events A and B, what is P(A ∩ B)?

Single Answer MCQ
Q-00078502
View explanation
Q50

A man speaks the truth 75% of the time. If he claims he rolled a six on a die, what is the probability it is actually a six?

Single Answer MCQ
Q-00078503
View explanation
Q51

Given that P(A) = 1/2 and P(B) = 1/3 for independent events A and B, what is P(A ∪ B)?

Single Answer MCQ
Q-00078504
View explanation
Q52

How do we obtain the probability of an event given a positive test result under Bayes' Theorem?

Single Answer MCQ
Q-00078505
View explanation
Q53

Which of the following pairs of events is independent?

Single Answer MCQ
Q-00078506
View explanation
Q54

If the probability of testing positive for a disease when one is actually sick is 0.95, but when one is not sick it is 0.1, what can be inferred using Bayes' Theorem?

Single Answer MCQ
Q-00078507
View explanation
Q55

What does it mean for events E and F to be independent?

Single Answer MCQ
Q-00078508
View explanation
Q56

What is Bayes' Theorem primarily used for?

Single Answer MCQ
Q-00078509
View explanation
Q57

If P(A) = 0.6 and P(B) = 0.4, and they are independent, what is P(B')?

Single Answer MCQ
Q-00078510
View explanation
Q58

In a scenario with two drugs, Drug A has 85% accuracy, while Drug B has 75%, what is crucial to consider with Bayes' Theorem?

Single Answer MCQ
Q-00078511
View explanation
Q59

Two dice are rolled. If A is the event that at least one die shows a 6 and B is the event that the sum is greater than 8, are A and B independent?

Single Answer MCQ
Q-00078512
View explanation
Q60

Given two events A and B, if A is a subset of B, how does Bayes' Theorem apply?

Single Answer MCQ
Q-00078513
View explanation
Q61

If the probability of event A occurring is 0.7 and the probability of event B occurring is 0.3, what is P(A ∩ B) if A and B are independent?

Single Answer MCQ
Q-00078514
View explanation
Q62

If you draw a card from a standard deck, what is the probability that it is a heart given that it is red?

Single Answer MCQ
Q-00078515
View explanation
Q63

Let E and F be events such that P(E) = 0.5 and P(E ∩ F) = 0.2. Are E and F independent?

Single Answer MCQ
Q-00078516
View explanation
Q64

In Bayesian analysis, what does the prior probability represent?

Single Answer MCQ
Q-00078517
View explanation
Q65

What is the probability of the complement of event A if A is independent with P(A) = 0.2?

Single Answer MCQ
Q-00078518
View explanation
Q66

What is the error in directly applying Bayes' Theorem without accounting for P(E)?

Single Answer MCQ
Q-00078519
View explanation
Q67

If two events E and F are such that P(E) = 1/4, P(F) = 1/2, and P(E ∩ F) = 1/8, are these events independent?

Single Answer MCQ
Q-00078520
View explanation
Q68

If event C occurs given events A and B, how can Bayes' Theorem be applied?

Single Answer MCQ
Q-00078521
View explanation
Q69

A box contains 3 red balls and 2 blue balls. If you draw two balls with replacement, what is the probability that both are red?

Single Answer MCQ
Q-00078522
View explanation
Q70

Which probability distribution is often connected with Bayes' Theorem?

Single Answer MCQ
Q-00078523
View explanation
Q71

What is the probability of getting at least one head when tossing two independent coins?

Single Answer MCQ
Q-00078524
View explanation
Q72

For two events A and B that are independent, how does it affect their Bayes' probabilities?

Single Answer MCQ
Q-00078525
View explanation
Q73

How does Bayes' Theorem refine initial probabilities based on new data?

Single Answer MCQ
Q-00078526
View explanation

Probability Practice Worksheets

Practice questions from Probability to improve accuracy and speed.

Probability - Practice Worksheet

This worksheet covers essential long-answer questions to help you build confidence in Probability from Mathematics Part - II for Class 12 (Mathematics).

Practice

Questions

1

Define conditional probability and provide its formula. Give a real-life example to illustrate conditional probability.

Conditional probability is the probability of an event occurring given that another event has already occurred. The formula for conditional probability is P(E|F) = P(E ∩ F) / P(F) where P(F) ≠ 0. An example is a scenario with two events: A being the event 'it is raining' and B being 'the ground is wet'. If it is known that it is raining (event F), the conditional probability of the ground being wet (event E) increases because rain causes the ground to become wet.

2

Explain the addition rule of probability. Provide an example that includes overlapping events.

The addition rule of probability states that for any two events A and B, the probability of A or B occurring is P(A ∪ B) = P(A) + P(B) - P(A ∩ B). This adjustment accounts for the double-counting of the intersection of A and B. For example, if P(A) = 0.5 and P(B) = 0.3, with P(A ∩ B) = 0.1, then P(A ∪ B) = 0.5 + 0.3 - 0.1 = 0.7.

3

Discuss the multiplication rule of probability for independent events. Illustrate with an example.

The multiplication rule states that for two independent events A and B, the probability of both A and B occurring is P(A ∩ B) = P(A) * P(B). For example, if the probability of rolling a 3 on one die is 1/6 and rolling a 4 on another die is also 1/6, the probability of rolling both a 3 and a 4 is (1/6) * (1/6) = 1/36.

4

Define the term 'random variable' and differentiate between discrete and continuous random variables.

A random variable is a variable whose value is subject to variations due to chance. Discrete random variables take on a countable number of distinct values (e.g., the number of heads in 5 coin tosses), while continuous random variables can take on an infinite number of values within a given range (e.g., the height of students).

5

Explain the concept of independent events with an example.

Two events are independent if the occurrence of one does not affect the probability of the other. For example, tossing a coin and rolling a die are independent events. The probability of getting heads on the coin toss and 4 on the die roll is P(Heads) * P(4) = (1/2) * (1/6) = 1/12.

6

What is the Binomial distribution? Provide a scenario where it applies.

The Binomial distribution models the number of successes in a fixed number of independent Bernoulli trials, where each trial has two possible outcomes. For example, if you flip a coin 10 times and count the number of heads, that scenario can be modeled using a binomial distribution with n = 10 trials and p = 0.5 as the probability of success (getting heads).

7

Define Bayes' theorem and explain its application with an example.

Bayes' theorem describes the probability of an event based on prior knowledge of conditions related to the event. It is expressed as P(Ei|A) = [P(A|Ei) * P(Ei)] / P(A). For example, if a test for a disease is 90% accurate (true positive) and the disease prevalence is 1%, we can use Bayes' theorem to find the probability that a person has the disease given a positive test result.

8

Illustrate the concept of expected value and its significance.

The expected value is the average of all possible values of a random variable, weighted by their probabilities. It provides a measure of the central tendency of the random variable. For example, in a game where you win $10 with a probability of 0.1 and lose $1 with a probability of 0.9, the expected value is E(X) = (10 * 0.1) + ((-1) * 0.9) = -$0.80, indicating an average loss.

9

What is the law of large numbers and how does it apply in probability?

The law of large numbers states that as the number of experiments increases, the sample mean (average) will converge to the expected value (population mean). For instance, flipping a fair coin many times will result in the proportion of heads approaching 0.5 (the theoretical probability) as the number of flips increases. This law reinforces the reliability of probability predictions over greater numbers of trials.

Probability - Mastery Worksheet

This worksheet challenges you with deeper, multi-concept long-answer questions from Probability to prepare for higher-weightage questions in Class 12.

Mastery

Questions

1

Consider two boxes. Box I has 3 red and 4 black balls, and Box II has 5 red and 6 black balls. A ball is drawn at random from one of the boxes. If the ball is red, what is the probability that it was drawn from Box II? Use Bayes' Theorem to derive the solution.

Let E1 be choosing Box I, E2 be choosing Box II, and A be drawing a red ball. Then P(E1) = P(E2) = 1/2, P(A|E1) = 3/7, P(A|E2) = 5/11. By Bayes' theorem: P(E2|A) = (P(E2) * P(A|E2)) / (P(E1) * P(A|E1) + P(E2) * P(A|E2)) Substituting values gives: P(E2|A) = (1/2 * 5/11) / [(1/2 * 3/7) + (1/2 * 5/11)] = 5/11 / [(3/7 + 5/11) / 2] = ... (calculate for final answer).

2

A die is rolled twice. What is the conditional probability that at least one of the rolls is a six, given that the sum of the two rolls is 9?

Let E be the event 'at least one six' and F be 'sum is 9'. Outcomes for F are: (3,6), (4,5), (5,4), (6,3). Favorable outcomes for E ∩ F are: (3,6) and (6,3). P(F) = 4/36 and P(E ∩ F) = 2/36. Then: P(E|F) = P(E ∩ F) / P(F) = (2/36) / (4/36) = ... = 1/2.

3

In a class of 30 students, 18 study Mathematics, 15 study Physics, and 10 study both subjects. What is the probability that a student chosen at random studies Mathematics given that he or she studies Physics?

Let A be studying Mathematics, B be studying Physics. We need P(A|B). The values are: P(A) = 18/30, P(B) = 15/30, P(A ∩ B) = 10/30. Using the formula: P(A|B) = P(A ∩ B) / P(B) = (10/30) / (15/30) = 10/15 = 2/3.

4

A family has two children. What is the probability that both children are girls given that at least one of them is a girl?

Let E be 'both children are girls', F be 'at least one child is a girl'. Possible outcomes are: GG, GB, BG, BB. Given F, the possible outcomes are GG, GB, BG. Favorable is GG. Thus: P(E|F) = P(E ∩ F) / P(F) = (1/4) / (3/4) = 1/3.

5

In an exam, a student is known to know the answer with probability 3/4 and guesses with probability 1/4. If the guessing has a success rate of 1/4, what is the probability that the student knew the answer given they answered correctly?

Let A be knowing the answer and C be answering correctly. Use Bayes' theorem: P(A|C) = (P(C|A)P(A)) / [P(C|A)P(A) + P(C|A')P(A')] P(C|A) = 1, P(C|A') = 1/4. Compute: P(A|C) = (1 * 3/4) / [(1 * 3/4) + (1/4 * 1/4)] = ...(substitute values to calculate).

6

A box contains 10 oranges and 5 apples. If two fruits are picked at random, what is the probability that both are apples?

Let A be selecting apples. Total ways to choose 2 fruits = C(15, 2), and ways to pick 2 apples = C(5, 2). Hence: P(A) = C(5, 2) / C(15, 2). Calculate: P(A) = (5! / (3!2!)) / (15! / (13!2!)) = ... (calculate final answer).

7

There are three bags. Bag X contains 2 white and 3 red balls, Bag Y contains 4 white and 1 red ball, and Bag Z contains 1 white and 4 red balls. If a ball is drawn and is found to be red, what is the probability that it was drawn from Bag Z?

Let A be drawing a red ball. Let E1, E2, E3 be events of choosing Bag X, Y, and Z respectively. Find: P(E1), P(E2), P(E3) = 1/3. Then, find P(A|E1), P(A|E2), P(A|E3). Use Bayes’ theorem: P(E3|A) = ... (substitute values accordingly).

8

A factory produces screws with 2 machines. Machine A produces 70% of screws, while Machine B produces 30%. The defect rates are 3% for A and 5% for B. If a screw is found to be defective, what is the probability it was produced by Machine A?

Let D be the event of 'defect' and E1, E2 be events of A and B. Calculate: P(D|E1), P(D|E2), P(E1), P(E2) and use Bayes' theorem: P(E1|D) = (P(E1)P(D|E1)) / [P(E1)P(D|E1) + P(E2)P(D|E2)] = ....

9

Two dice are thrown. What is the probability of getting a sum greater than 8 given that at least one die is a four?

Let E be 'sum > 8' and F be 'at least one die is 4'. Identify outcomes: F = {4,1}, {4,2}, {4,3}, {4,4}, {4,5}, {4,6}, {1,4}, {2,4}, {3,4}, {5,4}, {6,4}. Favorable outcomes: E ∩ F = {4,5}, {4,6}, {5,4}, {6,4}. Calculate: P(E|F) = P(E ∩ F)/P(F) =.. =>.

Probability - Challenge Worksheet

The final worksheet presents challenging long-answer questions that test your depth of understanding and exam-readiness for Probability in Class 12.

Challenge

Questions

1

Consider a dice game where Player A wins if they roll a sum greater than 10 when rolling two dice, while Player B wins if they roll an even sum. Evaluate the conditional probabilities of A winning given that B has scored a sum of 6.

Break down the probabilities of both players' outcomes using conditional probability concepts. Assess the independent events involved and calculate the conditional probabilities based on the given conditions.

2

A factory produces widgets that have a 2% defect rate. If 4 widgets are sampled, determine the probability that exactly 2 of them are defective, given that each widget is independent of the others.

Use the binomial distribution formula to find the likelihood of 2 defects in a 4 widget sample. Provide reasoning on the independence of each widget.

3

A school has a 70% graduation rate. If 3 students are selected at random, find the probability that at least one of them will not graduate.

Utilize the complement rule of probability for this calculation. Use the graduation rate to determine the probability of a student not graduating.

4

Evaluate the probability of drawing two red cards from a standard deck of playing cards if the first card drawn is returned to the deck before drawing the second card.

Calculate the probability of drawing a red card in both selections with replacement. Use multiplication of independent probabilities.

5

In a bag containing 5 black, 3 white, and 2 red balls, if two balls are drawn without replacement, determine the probability that both are of the same color.

Evaluate the possible combinations for drawing balls of the same color and calculate using the conditional probabilities.

6

An event occurs with a probability of 0.3. If two independent trials are conducted, find the probability that the event occurs in at least one of the trials.

Utilize the complement rule to find the probability that the event does not occur in either trial, then subtract from 1.

7

A survey indicates that 60% of people like chocolate and 50% of them like vanilla. If a person likes vanilla, what is the probability that they also like chocolate?

Apply Bayes' theorem to determine the conditional probability of liking chocolate given vanilla preference.

8

If a person rolls two dice, what is the probability that the sum of the rolls is 5, given that at least one of the dice shows 2?

Set up a conditional probability scenario and evaluate the specific outcomes where this condition holds true.

9

Given three boxes: Box A contains 2 gold coins, Box B contains 1 gold and 1 silver, and Box C contains 2 silver coins. A box is selected and a coin is drawn at random, which turns out to be gold. What is the probability that it was drawn from Box A?

Use Bayes’ Theorem to calculate the desired probability, covering all paths leading to the event of drawing a gold coin.

10

In an experiment, a fair die is thrown twice. Find the probability that the second roll is a 3 given that the first roll is even.

Analyze the conditional outcomes of rolling an even number and how they impact the probability of the second roll being 3.

Probability Formula Sheet

Quickly revise formulas and terms from Probability.

Formulas

1

P(E|F) = P(E ∩ F) / P(F) for P(F) ≠ 0

P(E|F) denotes the conditional probability of event E given that event F has occurred. It quantifies how the occurrence of F influences the likelihood of E.

2

P(E ∩ F) = P(E) * P(F|E)

This formula describes the joint probability of events E and F occurring together, calculated as the probability of E and the probability of F given E.

3

P(E ∪ F) = P(E) + P(F) - P(E ∩ F)

This formula calculates the probability of either event E or F occurring, ensuring that both events are not double-counted.

4

P(E') = 1 - P(E)

P(E') represents the probability of the complement event of E, meaning E does not occur. Useful for simplifying calculations.

5

P(E|F) + P(E'|F) = 1

This property reflects that the total probability for all outcomes must sum to 1, showing that if F occurs, either E must occur or not occur.

6

P(A ∪ B | F) = P(A | F) + P(B | F) - P(A ∩ B | F)

This formula extends the addition rule to conditional probabilities, allowing the calculation of the probability of either A or B given F.

7

P(A ∩ B) = P(A) * P(B|A)

It denotes the multiplication rule for the joint occurrence of events A and B, where A influences the occurrence of B.

8

If E and F are independent, P(E ∩ F) = P(E) * P(F)

This defines the condition for independence between two events, where the occurrence of one does not impact the probability of the other.

9

P(A | B) = P(A) when A and B are independent

When events A and B are independent, the occurrence of B does not change the probability of A.

10

Total Probability: P(A) = Σ P(E_i) * P(A|E_i)

This theorem is used to compute the total probability of event A based on partition events E_i, ensuring comprehensive coverage of all possibilities.

Equations

1

P(E|F) = P(E ∩ F) / P(F)

Defines conditional probability of E given F.

2

P(E') = 1 - P(E)

Probability of the complement of event E.

3

P(A ∪ B) = P(A) + P(B) - P(A ∩ B)

Union of events formula.

4

P(E|F) + P(E'|F) = 1

Sum of probabilities of event E and its complement given F.

5

P(E ∩ F) = P(E) * P(F|E)

Joint probability using conditional probability.

6

P(A ∩ B) = P(A) * P(B) if A and B are independent

Product of probabilities for independent events.

7

P(E|F) + P(E'|F) = 1

Total probability of all outcomes given F.

8

P(A ∪ B | F) = P(A | F) + P(B | F) - P(A ∩ B | F)

Conditional addition rule.

9

P(A) = Σ P(E_i) * P(A|E_i)

Total probability theorem.

10

P(E ∩ F) = P(E) * P(F|E) = P(F) * P(E|F)

Multiplication rule for joint events.

Probability FAQs

Explore key concepts of probability, including conditional probability, Bayes' theorem, and the multiplication rule in this comprehensive chapter for Class 12 Mathematics.

Probability is a branch of mathematics that deals with the likelihood of different outcomes in random experiments. It quantifies uncertainty and helps in determining how likely an event is to occur.
Conditional probability is the probability of an event occurring, given that another event has already occurred. It assesses how the likelihood of an event changes based on known outcomes.
Bayes' theorem provides a way to update the probability of a hypothesis based on new evidence. It relates the conditional and marginal probabilities of random events, allowing for better decision-making under uncertainty.
Conditional probability is calculated using the formula P(E|F) = P(E ∩ F) / P(F), where P(E|F) is the probability of event E given event F has occurred, provided P(F) is not zero.
The multiplication theorem states that the probability of the intersection of two events can be expressed as P(E ∩ F) = P(E) * P(F|E) or P(F) * P(E|F). This theorem is crucial for finding probabilities in complex scenarios.
Independent events are those whose occurrence does not affect the probability of each other. Mathematically, P(E ∩ F) = P(E) * P(F) for independent events.
For instance, if two dice are thrown, the probability of getting a total of 7 given that at least one die shows a 4 can be calculated using conditional probability.
A binomial distribution is a probability distribution that models the number of successes in a fixed number of independent trials, each with the same probability of success.
The addition rule states that the probability of either event A or event B occurring, P(A ∪ B), is given by P(A) + P(B) - P(A ∩ B), to account for any overlap.
Equally likely outcomes simplify probability calculations, as each outcome has the same chance of occurring. This is particularly useful in fair games and theoretical experiments.
Random variables serve as functions that assign numerical values to outcomes of random experiments, aiding in the calculation of probabilities and expected values.
Probability is used in various fields, including finance, healthcare, and engineering, to assess risks, make predictions, and guide decision-making under uncertainty.
The law of large numbers states that as the number of trials increases, the empirical probability converges to the theoretical probability. This principle is foundational in probability theory.
Probability distributions describe how probabilities are allocated across different outcomes. They are essential for understanding the behavior of random variables and for statistical inference.
Events in probability can be independent, dependent, or mutually exclusive, affecting how their probabilities combine. Understanding these interactions is crucial for accurate probability calculations.
Bayes' theorem allows for updating beliefs based on new evidence, making it a powerful tool in statistics, machine learning, and various fields for making informed decisions.
The sample space is the set of all possible outcomes of a probability experiment, which provides the context for calculating probabilities of specific events.
The multiplication rule is applied in scenarios involving multiple events, such as drawing cards from a deck or conducting surveys, to find joint probabilities and predict outcomes.
Mutually exclusive events cannot occur simultaneously. For example, when tossing a coin, getting heads and tails at the same time are mutually exclusive outcomes.
To determine if two events are independent, check if P(E ∩ F) = P(E) * P(F). If true, their outcomes do not influence each other.
A random experiment is a procedure that yields one of several possible outcomes, where the result cannot be predicted with certainty before it is performed.
Probability helps solve practical problems such as risk assessment in finance, predicting outcomes in sports, and determining the effectiveness of medical treatments.
Studying probability is essential for understanding uncertainty and variability in real-life situations, which is critical for making sound decisions in uncertain conditions.
One example is in medical diagnosis, where Bayes' theorem helps update the probability of a patient having a condition based on test results and prior probabilities.
Probability forms the foundation of statistics, allowing for the analysis of data, hypothesis testing, and the estimation of population parameters based on samples.
Discrete probability distributions deal with countable outcomes, while continuous distributions involve uncountable outcomes within a range, such as measurements of height.

Probability Downloads

Download worksheets, revision guides, formula sheets, and the official textbook PDF for Probability.

Probability Official Textbook PDF

Download the official NCERT/CBSE textbook PDF for Class 12 Mathematics.

Official PDFEnglish EditionNCERT Source

Probability Revision Guide

Use this one-page guide to revise the most important ideas from Probability.

One-page review

Probability Formula Sheet

Quickly revise the main formulas and terms from Probability.

Quick revision

Probability Practice Worksheet

Solve basic and application-based questions from Probability.

Basic comprehension exercises

Probability Mastery Worksheet

Work through mixed Probability questions to improve accuracy and speed.

Intermediate analysis exercises

Probability Challenge Worksheet

Try harder Probability questions that test deeper understanding.

Advanced critical thinking

Probability Flashcards

Test your memory with quick recall prompts from Probability.

These flash cards cover important concepts from Probability in Mathematics Part - II for Class 12 (Mathematics).

1/19

What is Probability?

1/19

Probability measures the likelihood of an event occurring, expressed as a number between 0 and 1.

How well did you know this?

Not at allPerfectly

2/19

What is a Sample Space (S)?

2/19

The sample space is the set of all possible outcomes of a random experiment.

How well did you know this?

Not at allPerfectly
Active

3/19

What is an Event in Probability?

Active

3/19

An event is a specific outcome or a set of outcomes from the sample space.

How well did you know this?

Not at allPerfectly

4/19

What is Conditional Probability P(E|F)?

4/19

P(E|F) is the probability of event E occurring given that event F has occurred.

5/19

How do you calculate P(E|F)?

5/19

P(E|F) = P(E ∩ F) / P(F), provided P(F) ≠ 0.

6/19

What are the three axioms of probability?

6/19

1) P(E) ≥ 0; 2) P(S) = 1; 3) For disjoint events A and B, P(A ∪ B) = P(A) + P(B).

7/19

What is the Addition Rule in Probability?

7/19

P(A ∪ B) = P(A) + P(B) - P(A ∩ B) for any two events A and B.

8/19

What is the Total Probability Theorem?

8/19

If F1, F2, ..., Fn are mutually exclusive events, P(E) = Σ P(E|Fi)P(Fi) for all i.

9/19

What defines Two Independent Events?

9/19

Two events A and B are independent if P(A ∩ B) = P(A)P(B).

10/19

What is the Probability of Complementary Events?

10/19

P(A') = 1 - P(A), where A' is the complement of event A.

11/19

What is a Binomial Distribution?

11/19

A distribution of outcomes of a fixed number of independent binary experiments.

12/19

How do you find the Mean of a Probability Distribution?

12/19

Mean (μ) = Σ [x * P(x)], where P(x) is the probability of outcome x.

13/19

How is Variance calculated in Probability?

13/19

Variance (σ²) = Σ [(x - μ)² * P(x)], measuring the spread of a distribution.

14/19

Calculate P(A|B) if P(A) = 1/4 and P(A ∩ B) = 1/8.

14/19

P(A|B) = P(A ∩ B) / P(B) = (1/8) / (1/4) = 1/2.

15/19

What is a common mistake in Conditional Probability?

15/19

Confusing P(E|F) with P(F|E); they are not the same unless E and F are independent.

16/19

What is the sample space of a single coin toss?

16/19

S = {Heads, Tails}.

17/19

What is the probability of getting Heads on a fair coin?

17/19

P(Heads) = 1/2.

18/19

What is the sample space for tossing three coins?

18/19

S = {HHH, HHT, HTH, THH, HTT, THT, TTH, TTT}.

19/19

What is Expected Value (E(X))?

19/19

E(X) = Σ [x * P(X=x)], giving the average outcome of a probability distribution.

Show all 19 flash cards

Practice mode

Live Academic Duel

Master Probability via Live Academic Duels

Challenge your classmates or test your individual retention on the core concepts of CBSE Class 12 Mathematics (Mathematics Part - II). Compete in speed-recall question rounds matched explicitly to the latest syllabus milestones for Probability.

CBSE-aligned questions
Instant speed-recall rounds

Quick, competitive practice on Probability with zero setup.