A rectangular container measuring 70 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 5 ℓ per minute was first turned on for 2 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
= 70 x 50 x 36
= 126000 cm
3 1 ℓ = 1000 cm
3 5 ℓ = 5000 cm
3 Volume of water filled by Tap Q
= 5000 x 7
= 35000 cm
3 Volume of water filled by Tap R
= 126000 - 35000
= 91000 cm
3 Rate in which Tap R fills the container
= 91000 ÷ 5
= 18200 cm3/min
18200 mℓ/min
= 18.2 ℓ/min
≈ 18.2 ℓ/min (Correct to 1 decimal place)
Answer(s): 18.2 ℓ/min