A rectangular tank measuring 70 cm by 54 cm by 34 cm was to be filled with water by two taps, C and D. Tap C which fills the tank at a rate of 6 ℓ per minute was first turned on for 4 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
= 70 x 54 x 34
= 128520 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap C
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap D
= 128520 - 42000
= 86520 cm
3 Rate in which Tap D fills the tank
= 86520 ÷ 3
= 28840 cm3/min
28840 mℓ/min
= 28.84 ℓ/min
≈ 28.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 28.8 ℓ/min