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.

[EX Q]: Problem: if 12 machine can finish a job in 40 days, then how many more machines would be needed to finish the job in one - fourth less time ?
Options: a. a. 4, b. b. 8, c. c. 10, d. d. 12, e. e. 16
[EX A]: a

[EX 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
[EX A]: d

[EX Q]: Problem: tom and marry each have a bag of marbles, each of which contains 4 red marbles, 10 blue marbles, and 6 yellow marbles. if tom and marry each select one marble from their respective bags, what is the probability that either tom or marry select a blue marble ?
Options: a. 1 / 7, b. 2 / 4, c. 3 / 4, d. 1 / 8, e. 1 / 16
[EX A]:
c