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, b, c can complete a piece of work in 24, 8,12 days. working together, they complete the same work in how many days ?
Options: a. 4, b. 4 / 5, c. 7 / 9, d. 10, e. 24 / 7

A: a
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Q: Problem: a shop owner professes to sell his articles at certain cost price but he uses false weights with which he cheats by 10 % while buying and by 20 % while selling. what is his percentage profit ?
Options: a. 10.22 %, b. 20.22 %, c. 21.22 %, d. 10 %, e. ca n ' t be calculated

A:
d
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