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: 30 pens and 75 pencils were purchased for 750. if the average price of a pencil was 2.00, find the average price of a pen.
Options: a. 20, b. 11, c. 12, d. 13, e. 14

A: a
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Q: Problem: if a train, travelling at a speed of 90 kmph, crosses a pole in 4 sec, then the length of train is ?
Options: a. 281, b. 125, c. 288, d. 100, e. 121

A: d
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Q: Problem: the ratio of three numbers is 1: 2: 3 and the sum of their squares is 2016. the sum of the numbers is ?
Options: a. a. 10, b. b. 12, c. c. 15, d. d. 14, e. e. 9

A:
b
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