A rectangular tank measuring 78 cm by 60 cm by 30 cm was to be filled with water by two taps, H and J. Tap H which fills the tank at a rate of 5 ℓ per minute was first turned on for 3 minutes before Tap J was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap H was first turned on, what is the rate at which Tap J fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 78 x 60 x 30
= 140400 cm
3 1 ℓ = 1000 cm
3 5 ℓ = 5000 cm
3 Volume of water filled by Tap H
= 5000 x 7
= 35000 cm
3 Volume of water filled by Tap J
= 140400 - 35000
= 105400 cm
3 Rate in which Tap J fills the tank
= 105400 ÷ 4
= 26350 cm3/min
26350 mℓ/min
= 26.35 ℓ/min
≈ 26.4 ℓ/min (Correct to 1 decimal place)
Answer(s): 26.4 ℓ/min