A rectangular container measuring 72 cm by 58 cm by 29 cm was to be filled with water by two taps, L and M. Tap L which fills the tank at a rate of 6 ℓ per minute was first turned on for 3 minutes before Tap M was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap L was first turned on, what is the rate at which Tap M fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 72 x 58 x 29
= 121104 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap L
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap M
= 121104 - 42000
= 79104 cm
3 Rate in which Tap M fills the container
= 79104 ÷ 4
= 19776 cm3/min
19776 mℓ/min
= 19.776 ℓ/min
≈ 19.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 19.8 ℓ/min