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: a cement mixture is composed of 3 elements. by weight, 1 / 2 of the mixture is sand, 1 / 5 of the mixture is water, and the remaining 15 pounds of the mixture is gravel. what is the weight of the entire mixture in pounds ?
Options: a. 30, b. 40, c. 50, d. 60, e. 80

A: c
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Q: Problem: a fruit - salad mixture consists of apples, peaches, and grapes in the ratio 6: 5: 4, respectively, by weight. if 60 pounds of the mixture is prepared, the mixture includes how many more pounds of apples than grapes ?
Options: a. 15, b. 12, c. 8, d. 6, e. 4

A: c
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Q: Problem: a can do a work in 15 days and b in 20 days. if they work on it together for 7 days, then the fraction of the work that is left is
Options: a. 8 / 17, b. 7 / 15, c. 3 / 15, d. 8 / 15, e. 11 / 60

A:
e
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