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?

50 litre/min

$\text{Tank capacity}=1500\text{ litres}.$

$\text{To empty the tank in }30\text{ minutes,}$

$\text{required outlet rate}=\frac{1500}{30}=50\text{ L/min}.$

$\text{Required outlet rate}=50\text{ L/min}.$