An inlet pipe can fill an empty tank in 40 minutes. An outlet pipe at the bottom drains water at 6 litres per minute. When the tank is empty and both pipes are opened together, the tank is full in 60 minutes. What is the capacity of the tank?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 720 litres
Let the capacity be \(C\) litres. The outlet takes away the difference between the inlet's rate and the net rate, and this difference is given as 6 litres per minute.
Inlet alone: \(\frac{C}{40}\) litres per minute
Both open: \(\frac{C}{60}\) litres per minute
Outlet rate \(\displaystyle =\frac{C}{40}-\frac{C}{60}=\frac{3C-2C}{120}=\frac{C}{120}\) litres per minute
\(\displaystyle \frac{C}{120}=6\), so \(C=720\)
The tank holds 720 litres.