Two pipes A and B can fill a tank in 40 minutes and 60 minutes respectively. Both pipes A and B are opened together. After some time pipe A is closed. If the tank is filled in 30 minutes, then after how many minutes the pipe A is turned off ?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 20
Work done by Pipe A in $t$ minutes,
Work By $A = \frac{t}{40}$
Work By $B = \frac{30}{60}=\frac{1}{2}$
$⇒\frac{t}{40}+\frac{1}{2}=1$
$⇒t=20$ minutes