A rectangular tank measuring 76 cm by 50 cm by 31 cm was to be filled with water by two taps, M and N. Tap M which fills the tank at a rate of 8 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
= 76 x 50 x 31
= 117800 cm
3 1 ℓ = 1000 cm
3 8 ℓ = 8000 cm
3 Volume of water filled by Tap M
= 8000 x 7
= 56000 cm
3 Volume of water filled by Tap N
= 117800 - 56000
= 61800 cm
3 Rate in which Tap N fills the tank
= 61800 ÷ 4
= 15450 cm3/min
15450 mℓ/min
= 15.45 ℓ/min
≈ 15.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 15.5 ℓ/min