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Two pipes P and Q can fill a tank in 26 minutes and 52 minutes respectively. Both the pipes are opened together for some time and then pipe P is closed. If the tank is filled in 26 minutes, then after how many minutes pipe P is closed?

Solution

✅ Correct Option: 3

Pipe P fills the tank in 26 minutes.

In 1 minute, Pipe P fills 126\frac{1}{26} of the tank.

Pipe Q fills the tank in 52 minutes.

In 1 minute, Pipe Q fills 152\frac{1}{52} of the tank.


Let Pipe P be closed after xx minutes.

Both pipes work together for xx minutes.

Only Pipe Q works for the remaining (26−x)(26 - x) minutes.


Work done by both pipes in xx minutes:

=x×(126+152)= x \times \left(\frac{1}{26} + \frac{1}{52}\right)

=x×(252+152)= x \times \left(\frac{2}{52} + \frac{1}{52}\right)

=x×352= x \times \frac{3}{52}

=3x52= \frac{3x}{52}


Work done by Pipe Q alone in (26−x)(26 - x) minutes:

=(26−x)×152= (26 - x) \times \frac{1}{52}

=26−x52= \frac{26 - x}{52}


Total work equals 1 full tank:

3x52+26−x52=1\frac{3x}{52} + \frac{26 - x}{52} = 1

3x+26−x52=1\frac{3x + 26 - x}{52} = 1

2x+2652=1\frac{2x + 26}{52} = 1

2x+26=522x + 26 = 52

2x=262x = 26

x=13x = 13

Therefore, Pipe P should be closed after 13 minutes.

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