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.

Q: Problem: if john makes a contribution to a charity fund at school, the average contribution size will increase by 50 % reaching $ 75 per person. if there were 1 other contributions made before john ' s, what is the size of his donation ?
Options: a. $ 100, b. $ 150, c. $ 200, d. $ 250, e. $ 450

A: a
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Q: Problem: rajani has to read a book of 445 pages. she has already read the first 157 pages of the book and if she reads 24 pages of the book everyday then how long will she take now to complete the book ?
Options: a. 25 days, b. 20 days, c. 46 days, d. 21 days, e. none of these

A: e
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Q: Problem: two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 22 seconds. the ratio of their speeds is ?
Options: a. 3 / 1, b. 3 / 1, c. 1 / 1, d. 3 / 5, e. 5 / 2

A:
c
****