A rectangular tank measuring 84 cm by 53 cm by 40 cm was to be filled with water by two taps, P and Q. Tap P which fills the tank at a rate of 8 ℓ per minute was first turned on for 3 minutes before Tap Q was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap P was first turned on, what is the rate at which Tap Q fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 84 x 53 x 40
= 178080 cm
3 1 ℓ = 1000 cm
3 8 ℓ = 8000 cm
3 Volume of water filled by Tap P
= 8000 x 7
= 56000 cm
3 Volume of water filled by Tap Q
= 178080 - 56000
= 122080 cm
3 Rate in which Tap Q fills the tank
= 122080 ÷ 4
= 30520 cm3/min
30520 mℓ/min
= 30.52 ℓ/min
≈ 30.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 30.5 ℓ/min