A rectangular tank measuring 82 cm by 56 cm by 30 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 2 minutes before Tap D was turned on as well. If the tank was filled to the brim in a total of 6 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
= 82 x 56 x 30
= 137760 cm
3 1 ℓ = 1000 cm
3 7 ℓ = 7000 cm
3 Volume of water filled by Tap C
= 7000 x 6
= 42000 cm
3 Volume of water filled by Tap D
= 137760 - 42000
= 95760 cm
3 Rate in which Tap D fills the tank
= 95760 ÷ 4
= 23940 cm3/min
23940 mℓ/min
= 23.94 ℓ/min
≈ 23.9 ℓ/min (Correct to 1 decimal place)
Answer(s): 23.9 ℓ/min