Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would take taken 6 hours more than A fill the cistern. How much time will be taken by A to fill the cistern separately?
1). 6 hours
2). 8 hours
3). 10 hours
4). 12 hours
⇒ Let the cistern be filled by pipe A alone in x hours.
⇒ Then, pipe B will fill it in (x + 6) hours
⇒ 1/x + 1/(x + 6) = ¼ (x + 6 + x)/(x (x + 6)) = 1/4
⇒ x2 - 2x - 24 = 0 (x - 6) (x + 4) = 0
⇒ x = 6, - 4 [Ignoring the -ve value of x]
X = 6 hours will be the required ans.