A rectangular tank measuring 85 cm by 50 cm by 40 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 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
= 85 x 50 x 40
= 170000 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
= 170000 - 42000
= 128000 cm
3 Rate in which Tap D fills the tank
= 128000 ÷ 5
= 25600 cm3/min
25600 mℓ/min
= 25.6 ℓ/min
≈ 25.6 ℓ/min (Correct to 1 decimal place)
Answer(s): 25.6 ℓ/min