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

Q: Problem: two pipes a and b can separately fill a cistern in 60 minutes and 75 minutes respectively . there is a third pipe in the bottom of the cistern to empty it . if all the three pipes are simultaneously opened , then the cistern is full in 50 minutes . in how much time , the third pipe alone can empty the cistern ?

A: 100 min
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Q: Problem: the smallest value of n , for which n + 2 is not a prime number , is

A: 2,4
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Q: Problem: surface area of a sphere is 2464 cm 2 . if its radius is doubled , then the surface area of the new sphere will be

A:
9856 cm 2', 'd ) 19712 cm 2', 'e ) none'
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