A rectangular container measuring 81 cm by 60 cm by 29 cm was to be filled with water by two taps, G and H. Tap G which fills the tank at a rate of 9 ℓ per minute was first turned on for 3 minutes before Tap H was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap G was first turned on, what is the rate at which Tap H fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 81 x 60 x 29
= 140940 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap G
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap H
= 140940 - 63000
= 77940 cm
3 Rate in which Tap H fills the container
= 77940 ÷ 4
= 19485 cm3/min
19485 mℓ/min
= 19.485 ℓ/min
≈ 19.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 19.5 ℓ/min