Question

Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:
A.1(13/17) hours
B.2(8/11) hours
C.3(9/17) hours
D.4(1/2) hours

Answer 1

the answer of this question is

option C

Answer 2

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(A+B)'s 2 hour's work when opened =

$\begin{aligned}</p><p>\frac{1}{6}+\frac{1}{4} = \frac{5}{12} \\</p><p></p><p>(A+B)'s \text{ 4 hour's work} = \frac{5}{12}*2 \\</p><p>= \frac{5}{6}</p><p></p><p>\text{Remaining work = } 1-\frac{5}{6} \\</p><p>= \frac{1}{6} \\</p><p></p><p>\text{Now, its A turn in 5 th hour} \\</p><p>\frac{1}{6} \text{ work will be done by A in 1 hour}\\</p><p>\text{Total time = } \bf \huge \: 4+1 = 5 hours </p><p>\end{aligned}$