A rectangular tank measuring 86 cm by 50 cm by 28 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 5 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
= 86 x 50 x 28
= 120400 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap K
= 9000 x 5
= 45000 cm
3 Volume of water filled by Tap L
= 120400 - 45000
= 75400 cm
3 Rate in which Tap L fills the tank
= 75400 ÷ 1
= 75400 cm3/min
75400 mℓ/min
= 75.4 ℓ/min
≈ 75.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 75.4 ℓ/min