A rectangular tank measuring 78 cm by 50 cm by 36 cm was to be filled with water by two taps, Q and R. Tap Q which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap R was turned on as well. If the tank was filled to the brim in a total of 5 minutes from the time when Tap Q was first turned on, what is the rate at which Tap R fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 78 x 50 x 36
= 140400 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap Q
= 9000 x 5
= 45000 cm
3 Volume of water filled by Tap R
= 140400 - 45000
= 95400 cm
3 Rate in which Tap R fills the tank
= 95400 ÷ 1
= 95400 cm3/min
95400 mℓ/min
= 95.4 ℓ/min
≈ 95.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 95.4 ℓ/min