Pipe A can fill a tank in 16 minutes and pipe B empties it in 24 minutes. If both the pipes are opened together, after how many minutes should B be closed, so that the tank is filled in 30 minutes?

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Question

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SSC MTS Memory Based Test (Based on: 5 September 2023 Shift 1)

Answer 1

Given∶

Time taken by pipe A to fill the tank = 16 minutes

Time taken by pipe B to empty the tank = 24 minutes

Calculation∶

Efficiency of pipe A = 1/16

Efficiency of pipe B = 1/24

Filling of tank by pipe A in 30 minutes = 30 × 1/16 = 15/8

Amount of water filled by pipe A which is in excess after filling the tank = 15/8 – 1 = 7/8

This excess water is emptied by pipe B when they open together.

Time taken by pipe B to empty excess water = (7/8) / (1/24) = 21 minutes

Alternate Solution∶

Amount of water filled by pipe A in 30 minutes = 3 × 30 = 90

Excess water filled by pipe A = 90 – 48 = 42

This excess water is emptied by pipe B when they open together.

Time taken by pipe B to empty excess water = 42/2 = 21 minutes