A rectangular container measuring 72 cm by 50 cm by 31 cm was to be filled with water by two taps, K and L. Tap K which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap L was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap K was first turned on, what is the rate at which Tap L fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 72 x 50 x 31
= 111600 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap K
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap L
= 111600 - 63000
= 48600 cm
3 Rate in which Tap L fills the container
= 48600 ÷ 3
= 16200 cm3/min
16200 mℓ/min
= 16.2 ℓ/min
≈ 16.2 ℓ/min (Correct to 1 decimal place)
Answer(s): 16.2 ℓ/min