A rectangular tank measuring 77 cm by 51 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 4 minutes before Tap Q was turned on as well. If the tank was filled to the brim in a total of 6 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
= 77 x 51 x 40
= 157080 cm
3 1 ℓ = 1000 cm
3 8 ℓ = 8000 cm
3 Volume of water filled by Tap P
= 8000 x 6
= 48000 cm
3 Volume of water filled by Tap Q
= 157080 - 48000
= 109080 cm
3 Rate in which Tap Q fills the tank
= 109080 ÷ 2
= 54540 cm3/min
54540 mℓ/min
= 54.54 ℓ/min
≈ 54.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 54.5 ℓ/min