Inlet A is four times faster than inlet B to fill a tank.

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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?

1. 10 min
2. 12 min
3. 15 min
4. 14 min

Correct Option: B

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