A rectangular tank measuring 75 cm by 60 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 7 ℓ per minute was first turned on for 3 minutes before Tap D was turned on as well. If the tank was filled to the brim in a total of 5 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
= 75 x 60 x 31
= 139500 cm
3 1 ℓ = 1000 cm
3 7 ℓ = 7000 cm
3 Volume of water filled by Tap C
= 7000 x 5
= 35000 cm
3 Volume of water filled by Tap D
= 139500 - 35000
= 104500 cm
3 Rate in which Tap D fills the tank
= 104500 ÷ 2
= 52250 cm3/min
52250 mℓ/min
= 52.25 ℓ/min
≈ 52.3 ℓ/min (Correct to 1 decimal place)
Answer(s): 52.3 ℓ/min