Inlet A is four times faster than inlet B to fill a tank. If A alone can fill it in 15 min, how long will it take if both the pipes are opened together?

10 min
12 min
15 min
14 min

Correct Answer: 12 min

Explanation:

Time taken by A to fill the tank, m = 15 min
∴ Time taken by B to fill the tank, n = 15 x 4 = 60
∴ Required time taken m x n/(m + n)
= (15 x 60)/(15 + 60) = (15 x 60)/75 = 12 min

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