A rectangular tank measuring 87 cm by 59 cm by 40 cm was to be filled with water by two taps, Y and Z. Tap Y which fills the tank at a rate of 6 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 7 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
= 87 x 59 x 40
= 205320 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap Y
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap Z
= 205320 - 42000
= 163320 cm
3 Rate in which Tap Z fills the tank
= 163320 ÷ 4
= 40830 cm3/min
40830 mℓ/min
= 40.83 ℓ/min
≈ 40.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 40.8 ℓ/min