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 goods train runs at the speed of 72 kmph and crosses a 250 m long platform in 24 seconds. what is the length of the goods train ?
Options: a. 230 m, b. 240 m, c. 260 m, d. 270 m, e. none of these

A: a
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Q: Problem: a can finish a work in 60 days, b in 9 days and c in 2 days, b and c start the work but are forced to leave after 3 days. the remaining work was done by a in ?
Options: a. 10 days, b. 25 days, c. 6 days, d. 7 days, e. 8 days

A: b
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Q: Problem: if a person walks at 20 km / hr instead of 10 km / hr, he would have walked 40 km more. the actual distance traveled by him is ?
Options: a. 40 km, b. 76 km, c. 18 km, d. 16 km, e. 97 km

A:
a
****