A rectangular container measuring 81 cm by 52 cm by 40 cm was to be filled with water by two taps, U and V. Tap U which fills the tank at a rate of 6 ℓ per minute was first turned on for 4 minutes before Tap V was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap U was first turned on, what is the rate at which Tap V fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 81 x 52 x 40
= 168480 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap U
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap V
= 168480 - 42000
= 126480 cm
3 Rate in which Tap V fills the container
= 126480 ÷ 3
= 42160 cm3/min
42160 mℓ/min
= 42.16 ℓ/min
≈ 42.2 ℓ/min (Correct to 1 decimal place)
Answer(s): 42.2 ℓ/min