Question

Two taps a and b can fill a water tank in 5 and 4 hours respectively. If they are turned up alternatively for one hour each (staring with tap a), find the time taken to fill the tank.

Answer 1

Let the capacity of tank = LCM(6,4) = 12L

Pipe A will fill 12/6 = 2L per hour

Pipe B will fill 12/4 = 3L per hour

If A is opened first for 1 hour and then B is opened for 1 hour, they will fill 5L in 2 hours.

Number of such cycles = [12/5] = 2 or 4 hours.

Remaining 2L will be filled by A in 1 hour.

=> Total time taken = 4 + 1 = 5 hours...

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