A rectangular tank measuring 90 cm by 54 cm by 23 cm was to be filled with water by two taps, X and Y. Tap X which fills the tank at a rate of 5 ℓ per minute was first turned on for 2 minutes before Tap Y was turned on as well. If the tank was filled to the brim in a total of 6 minutes from the time when Tap X was first turned on, what is the rate at which Tap Y fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 90 x 54 x 23
= 111780 cm
3 1 ℓ = 1000 cm
3 5 ℓ = 5000 cm
3 Volume of water filled by Tap X
= 5000 x 6
= 30000 cm
3 Volume of water filled by Tap Y
= 111780 - 30000
= 81780 cm
3 Rate in which Tap Y fills the tank
= 81780 ÷ 4
= 20445 cm3/min
20445 mℓ/min
= 20.445 ℓ/min
≈ 20.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 20.4 ℓ/min