Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Example Input: Problem: by selling 20 pencils for a rupee a man loses 30 %. how many for a rupee should he sell in order to gain 30 % ?
Options: a. 8.56, b. 10.75, c. 14.5, d. 16.5, e. 11.4
Example Output: b

Example Input: Problem: in a group of 100 people, 90 have an age of more 30 years, and the others have an age of less than 20 years. if a person is selected at random from this group, what is the probability the person ' s age is less than 20 ?
Options: a. 0.1, b. 0.55, c. 0.65, d. 0.75, e. 0.85
Example Output: a

Example Input: Problem: the average of first 5 multiples of 5 is
Options: a. 3, b. 6, c. 9, d. 12, e. 15
Example Output:
e