Tap A and tap B together fill an empty tank of capacity 1500 litres in 1 hour. At what rate should the outlet pipe release the water to empty the tank in half an hour?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 50 litre/min
To empty the full tank on its own (with the taps closed), the outlet pipe must release all 1500 litres in half an hour, that is in 30 minutes:
\( \displaystyle \text{Rate} = \frac{1500}{30} = 50 \text{ litre/min} \)
The taps fill the tank at \(\frac{1500}{60} = 25\) litre/min (Option 4); that is the filling rate, not the rate needed to empty the tank in half an hour.