A rectangular tank measuring 80 cm by 57 cm by 31 cm was to be filled with water by two taps, C and D. Tap C which fills the tank at a rate of 5 ℓ per minute was first turned on for 2 minutes before Tap D was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap C was first turned on, what is the rate at which Tap D fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 80 x 57 x 31
= 141360 cm
3 1 ℓ = 1000 cm
3 5 ℓ = 5000 cm
3 Volume of water filled by Tap C
= 5000 x 7
= 35000 cm
3 Volume of water filled by Tap D
= 141360 - 35000
= 106360 cm
3 Rate in which Tap D fills the tank
= 106360 ÷ 5
= 21272 cm3/min
21272 mℓ/min
= 21.272 ℓ/min
≈ 21.3 ℓ/min (Correct to 1 decimal place)
Answer(s): 21.3 ℓ/min