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Pipes and Cistern - General Aptitude

Q1:

Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?

A 1 hours

B 2 hours

C 6 hours

D 8 hours

ANS:C - 6 hours

Let the cistern be filled by pipe A alone in x hours. Then, pipe B will fill it in (x + 6) hours.

1 + 1 = 1
x (x + 6) 4
x + 6 + x = 1
x(x + 6) 4
x2 - 2x - 24 = 0 (x -6)(x + 4) = 0 x = 6.     [neglecting the negative value of x]