Attempt the question, check the explanation, and continue with similar questions to build confidence before exams.
1 + 2 + 4 + 8 + 16
2 + 3 + 5 + 7
1 + 1/2 + 1/4 + ...
2 + 4 + 8 + ... + 2^5
Continue with nearby questions to strengthen the same chapter concept while you still have the context fresh in mind.