A rectangular tank measuring 89 cm by 59 cm by 20 cm was to be filled with water by two taps, R and S. Tap R which fills the tank at a rate of 9 ℓ per minute was first turned on for 2 minutes before Tap S was turned on as well. If the tank was filled to the brim in a total of 6 minutes from the time when Tap R was first turned on, what is the rate at which Tap S fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 89 x 59 x 20
= 105020 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap R
= 9000 x 6
= 54000 cm
3 Volume of water filled by Tap S
= 105020 - 54000
= 51020 cm
3 Rate in which Tap S fills the tank
= 51020 ÷ 4
= 12755 cm3/min
12755 mℓ/min
= 12.755 ℓ/min
≈ 12.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 12.8 ℓ/min