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: two trains are moving in opposite directions at 60 km / hr and 90 km / hr. their lengths are 1.15 km and 0.6 km respectively. the time taken by the slower train to cross the faster train in seconds is ?
Options: a. 42, b. 9, c. 7, d. 67, e. 15

A: a
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Q: Problem: the arithmetic mean and standard deviation of a certain normal distribution are 14.5 and 1.7, respectively. what value is exactly 2 standard deviations less than the mean ?
Options: a. 10.5, b. 11, c. 11.1, d. 12, e. 12.5

A: c
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Q: Problem: sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. sandy attempts 30 sums and obtains 50 marks. how many sums did sandy get correct ?
Options: a. 20, b. 22, c. 24, d. 26, e. 28

A:
b
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