A rectangular tank measuring 90 cm by 50 cm by 27 cm was to be filled with water by two taps, Y and Z. Tap Y which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap Z was turned on as well. If the tank was filled to the brim in a total of 5 minutes from the time when Tap Y was first turned on, what is the rate at which Tap Z fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 90 x 50 x 27
= 121500 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap Y
= 9000 x 5
= 45000 cm
3 Volume of water filled by Tap Z
= 121500 - 45000
= 76500 cm
3 Rate in which Tap Z fills the tank
= 76500 ÷ 1
= 76500 cm3/min
76500 mℓ/min
= 76.5 ℓ/min
≈ 76.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 76.5 ℓ/min