A rectangular container measuring 72 cm by 56 cm by 37 cm was to be filled with water by two taps, Q and R. Tap Q which fills the tank at a rate of 6 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
= 72 x 56 x 37
= 149184 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap Q
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap R
= 149184 - 42000
= 107184 cm
3 Rate in which Tap R fills the container
= 107184 ÷ 3
= 35728 cm3/min
35728 mℓ/min
= 35.728 ℓ/min
≈ 35.7 ℓ/min (Correct to 1 decimal place)
Answer(s): 35.7 ℓ/min