A tank holds 1200 litres of water when full. An inlet pipe lets water in at 20 litres per minute, and an outlet pipe lets water out at 12 litres per minute. The tank is empty and both pipes are opened at the same time. How long will it take to fill the tank?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2 hours 30 minutes
With both pipes open, the tank gains the inflow minus the outflow every minute.
Net gain \(=20-12=8\) litres per minute
Time \(\displaystyle =\frac{1200}{8}=150\) minutes
\(150\) minutes \(=2\) hours \(30\) minutes
The tank is full in 2 hours 30 minutes.