A rectangular tank measuring 89 cm by 52 cm by 20 cm was to be filled with water by two taps, M and N. Tap M which fills the tank at a rate of 9 ℓ per minute was first turned on for 3 minutes before Tap N was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap M was first turned on, what is the rate at which Tap N fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 89 x 52 x 20
= 92560 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap M
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap N
= 92560 - 63000
= 29560 cm
3 Rate in which Tap N fills the tank
= 29560 ÷ 4
= 7390 cm3/min
7390 mℓ/min
= 7.39 ℓ/min
≈ 7.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 7.4 ℓ/min