A rectangular container measuring 70 cm by 56 cm by 20 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 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 container
= 70 x 56 x 20
= 78400 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
= 78400 - 35000
= 43400 cm
3 Rate in which Tap Z fills the container
= 43400 ÷ 1
= 43400 cm3/min
43400 mℓ/min
= 43.4 ℓ/min
≈ 43.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 43.4 ℓ/min