lets find the time to fill empty tank...

Number Theory Level 1

Pipe A can fill a tank in 15 min, pipe B in 18 min and a leak can empty the tank in 90 min. If all of them work together, find the time taken to fill the empty tank?


The answer is 9.

Sunitha P by sunitha p , 28, India

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2 solutions

Sunitha P
Mar 13, 2014

Net part filled in 1 min = (1/15 + 1/18 – 1/90) = 1/9 So, the empty tank will be filled in 9 min.

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a simple amazing solution

Neri Danessa Labayog - 7 years, 2 months ago

LET A,B,C be the pipes..

V= volume of the tank

dA/dt = rate of pipe A = V/15 dB/dt = rate of pipe B = V/18 dC/dt = rate of pipe C = - V/90 dT/dt = total rate

since the volume is not given we can assume that the volume of the tank is 1.

therefore: dT/dt = volume/ total time = 1/ total time

1/15 +1/18 - 1/90 = 1/ total time

total time = 9

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i prefer this sol.

Khadija Aijaz - 7 years, 2 months ago

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