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Flash Cards: Permutations and Combinations

This chapter introduces the concepts of permutations and combinations, essential for counting arrangements and selections in mathematics.

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Permutations and Combinations - Flash Cards

These flash cards cover important concepts from Permutations and Combinations in Mathematics for Class 11 (Mathematics).

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What is the Fundamental Principle of Counting?

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It states that if an event can occur in m ways and another event can occur in n ways, then the total number of occurrences is m × n.

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What is a permutation?

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A permutation is an arrangement of objects in a specific order.

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What is a combination?

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A combination is a selection of objects without regard to the order.

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What is the formula for permutations of n objects taken r at a time?

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The formula is P(n, r) = n! / (n - r)!, where n! denotes the factorial of n.

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What is the formula for combinations of n objects taken r at a time?

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The formula is C(n, r) = n! / [r!(n - r)!], where n! is the factorial of n.

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How many ways can the letters of 'DOG' be arranged?

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The letters can be arranged in 3! = 6 ways: DOG, DGO, ODG, OGD, GDO, GOD.

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How many ways can 2 fruits be chosen from {Apple, Banana, Cherry}?

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The fruits can be chosen in C(3, 2) = 3 ways: {Apple, Banana}, {Apple, Cherry}, {Banana, Cherry}.

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What is a factorial?

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The factorial of a non-negative integer n, denoted n!, is the product of all positive integers up to n.

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What is a common mistake in permutations?

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Not accounting for repetition of objects can lead to incorrect calculations.

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How do you calculate permutations of identical objects?

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Use the formula P(n; n1, n2,..., nk) = n! / (n1! n2!... nk!), where n1, n2, etc. are counts of identical objects.

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When do we use the Counting Principle?

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We use it to determine the total number of outcomes in sequential events.

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Does order matter in combinations?

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No, order does not matter in combinations; it does in permutations.

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How many signals can be generated with 4 flags using 2?

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Using the permutation principle, the number of signals = 4 × 3 = 12.

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How many 2-digit even numbers can be formed from {1, 2, 3, 4, 5}?

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There are 10 ways: 12, 14, 22, 24, 32, 34, 42, 44, 52, 54.

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How many different signals can be made using 5 flags?

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Total signals = P(5, 2) + P(5, 3) + P(5, 4) + P(5, 5) = 20 + 60 + 120 + 120 = 320.

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What rule is applied for permutations with no repetition?

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Use the decreasing number of choices for each position, as shown in 4!

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How to count arrangements with repetition?

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For n positions with k different choices, the total arrangements are k^n.

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Where are combinations used?

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Combinations are used in scenarios like lottery games or selecting committee members.