Tips on Solving Problems Based on Pipes & Cisterns

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TIPS on cracking Aptitude Questions on Pipes and
Cisterns
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Tip 1 Assume that the filling rate or the
emptying rate for each pipe is constant
Question Pipe A can fill the tank in 20 hours
while Pipe B alone can fill it in 30 hours and
Pipe C can empty the tank in 40 hours. If all the
pipes are opened together, in how long will the
tank be full? Solution Let the capacity of the
tank be C liters Fill rate of A, Fa C/20 liters
per hr Fill rate of B, Fb C/30 liters per
hr Fill rate of C, Fc - C/40 liters per hr
Negative since this pipe is emptying the
tank Let t be the time taken to fill the tank to
maximum capacity. t x Fa Fb Fc C gt t
120/7 hrs Question A pump can fill a tank with
water in 2 hours. Because of a leak, it took 2.5
hours to fill the tank. If the pump is turned
off, how long will it take to empty the
tank? Solution Fill rate of pipe, Fp C/2
liters per hr Let the fill rate of the leak be
FL 2.5 x Fp FL C gt FL - C/10 With the
pump turned off, it would take 10 hrs for the
leak to empty the tank.
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