A rectangular tank measuring 86 cm by 53 cm by 21 cm was to be filled with water by two taps, L and M. Tap L which fills the tank at a rate of 6 ℓ per minute was first turned on for 4 minutes before Tap M was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap L was first turned on, what is the rate at which Tap M fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 86 x 53 x 21
= 95718 cm
3 1 ℓ = 1000 cm
3 6 ℓ = 6000 cm
3 Volume of water filled by Tap L
= 6000 x 7
= 42000 cm
3 Volume of water filled by Tap M
= 95718 - 42000
= 53718 cm
3 Rate in which Tap M fills the tank
= 53718 ÷ 3
= 17906 cm3/min
17906 mℓ/min
= 17.906 ℓ/min
≈ 17.9 ℓ/min (Correct to 1 decimal place)
Answer(s): 17.9 ℓ/min