A rectangular container measuring 79 cm by 51 cm by 30 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 4 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 container
= 79 x 51 x 30
= 120870 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap M
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap N
= 120870 - 42000
= 78870 cm
3 Rate in which Tap N fills the container
= 78870 ÷ 3
= 26290 cm3/min
26290 mℓ/min
= 26.29 ℓ/min
≈ 26.3 ℓ/min (Correct to 1 decimal place)
Answer(s): 26.3 ℓ/min