A rectangular tank measuring 74 cm by 56 cm by 30 cm was to be filled with water by two taps, V and W. Tap V which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap W was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap V was first turned on, what is the rate at which Tap W fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 74 x 56 x 30
= 124320 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap V
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap W
= 124320 - 63000
= 61320 cm
3 Rate in which Tap W fills the tank
= 61320 ÷ 3
= 20440 cm3/min
20440 mℓ/min
= 20.44 ℓ/min
≈ 20.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 20.4 ℓ/min