A rectangular container measuring 78 cm by 53 cm by 39 cm was to be filled with water by two taps, A and B. Tap A which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap B was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap A was first turned on, what is the rate at which Tap B fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the container
= 78 x 53 x 39
= 161226 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap A
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap B
= 161226 - 63000
= 98226 cm
3 Rate in which Tap B fills the container
= 98226 ÷ 3
= 32742 cm3/min
32742 mℓ/min
= 32.742 ℓ/min
≈ 32.7 ℓ/min (Correct to 1 decimal place)
Answer(s): 32.7 ℓ/min