The task is to generate the correct answer for a given math problem.

Q: Problem: a dealer purchases 15 articles for rs . 25 and sells 12 articles for rs . 32 . find the profit percentage ?

A: 60 
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Q: Problem: the diameter of the driving wheel of a bus in 140 cm . how many revolutions per minute must the wheel make in order to keep a speed of 33 kmph ?

A: 125
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Q: Problem: bill downloads the movierevenge of the avengersto his computer in 2.5 hours , using a download manager that downloads from 3 sources marked a , b and c . each source provides download at a constant rate , but the rates of different sources are not necessarily identical . if the movie was downloaded from sources a and c alone , it would take 4 hours to complete the download . the next day , source b is available , but the other sources are inactive . how long will it take to download the trailer of the movie , a file that is 10 times smaller , from source b alone ?

A:
40 minutes
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