Question 73

To fill a certain tank, pipes A, B and C take 20 minutes, 15 minutes and 12 minutes respectively. If the three pipes are opened every alternate minute, how long will it take to fill the tank?

Solution

Part filled by 3 pipes in 3 minutes = $$\frac{1}{20} + \frac{1}{15} + \frac{1}{12} = \frac{3 + 4 + 5}{60} = \frac{1}{5}$$

1/5th of the tank is filled in 3 minutes then whole tank is filled in 5 x 3 = 15min

Hence, option D is the correct answer.

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