A rectangular tank measuring 90 cm by 59 cm by 24 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 tank
= 90 x 59 x 24
= 127440 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
= 127440 - 63000
= 64440 cm
3 Rate in which Tap L fills the tank
= 64440 ÷ 3
= 21480 cm3/min
21480 mℓ/min
= 21.48 ℓ/min
≈ 21.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 21.5 ℓ/min