A rectangular tank measuring 78 cm by 58 cm by 40 cm was to be filled with water by two taps, M and N. Tap M which fills the tank at a rate of 6 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 5 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
= 78 x 58 x 40
= 180960 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap M
= 6000 x 5
= 30000 cm
3 Volume of water filled by Tap N
= 180960 - 30000
= 150960 cm
3 Rate in which Tap N fills the tank
= 150960 ÷ 2
= 75480 cm3/min
75480 mℓ/min
= 75.48 ℓ/min
≈ 75.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 75.5 ℓ/min