A rectangular tank measuring 78 cm by 55 cm by 23 cm was to be filled with water by two taps, Y and Z. Tap Y which fills the tank at a rate of 7 ℓ per minute was first turned on for 3 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
= 78 x 55 x 23
= 98670 cm
3 1 ℓ = 1000 cm
3 7 ℓ = 7000 cm
3 Volume of water filled by Tap Y
= 7000 x 5
= 35000 cm
3 Volume of water filled by Tap Z
= 98670 - 35000
= 63670 cm
3 Rate in which Tap Z fills the tank
= 63670 ÷ 2
= 31835 cm3/min
31835 mℓ/min
= 31.835 ℓ/min
≈ 31.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 31.8 ℓ/min