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?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 13 minutes
Pipe Q stays open for the whole 26 minutes, and pipe P only for the first x minutes. P fills \(\frac{1}{26}\) of the tank per minute and Q fills \(\frac{1}{52}\):
\( \displaystyle \frac{x}{26} + \frac{26}{52} = 1 \)
\( \displaystyle \frac{x}{26} = \frac{1}{2} \)
\(x = 13\)
So pipe P is closed after 13 minutes.