A rectangular container measuring 75 cm by 60 cm by 27 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 7 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 container
= 75 x 60 x 27
= 121500 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap Q
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap R
= 121500 - 63000
= 58500 cm
3 Rate in which Tap R fills the container
= 58500 ÷ 3
= 19500 cm3/min
19500 mℓ/min
= 19.5 ℓ/min
≈ 19.5 ℓ/min (Correct to 1 decimal place)
Answer(s): 19.5 ℓ/min