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 a sum of money doubles itself in 20 years at simple interest, the ratepercent per annum is
Options: a. 12, b. 12.5, c. 13, d. 5, e. 14

A: d
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Q: Problem: a train traveling at 72 kmph crosses a platform in 33 seconds and a man standing on the platform in 18 seconds. what is the length of the platform in meters ?
Options: a. 240 meters, b. 360 meters, c. 420 meters, d. 300 meters, e. can not be determined

A: d
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Q: Problem: there are 4 people of different heights standing in order of increasing height. the difference is 2 inches between the first person and the second person, and also between the second person and the third person. the difference between the third person and the fourth person is 6 inches and the average height is 78. how tall is the fourth person ?
Options: a. 82, b. 84, c. 86, d. 88, e. 90

A:
b
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