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 copy machine, working at a constant rate, makes 35 copies per minute. a second copy machine, working at a constant rate, makes 65 copies per minute. working together at their respective rates, how many copies do the two machines make in half an hour ?
Options: a. 3,000, b. 2,700, c. 4,500, d. 5,400, e. 324,000

A: a
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Q: Problem: there are 7 pairs of socks and 2 socks are worn from that such that the pair of socks worn are not of the same pair. what is the number of pair that can be formed.
Options: a. 40, b. 49, c. 41, d. 56, e. 42

A: e
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Q: Problem: if the radius of a cylinder is made 3 times and height is doubled, what is the new volume of the cylinder divided by the old one ?
Options: a. 18., b. 2., c. 6., d. 4., e. 10.

A:
a
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