A rectangular container measuring 87 cm by 51 cm by 20 cm was to be filled with water by two taps, P and Q. Tap P which fills the tank at a rate of 9 ℓ per minute was first turned on for 3 minutes before Tap Q was turned on as well. If the tank was filled to the brim in a total of 5 minutes from the time when Tap P was first turned on, what is the rate at which Tap Q fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 87 x 51 x 20
= 88740 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap P
= 9000 x 5
= 45000 cm
3 Volume of water filled by Tap Q
= 88740 - 45000
= 43740 cm
3 Rate in which Tap Q fills the container
= 43740 ÷ 2
= 21870 cm3/min
21870 mℓ/min
= 21.87 ℓ/min
≈ 21.9 ℓ/min (Correct to 1 decimal place)
Answer(s): 21.9 ℓ/min