A rectangular tank 80 cm by 50 cm by 48 cm was 20% filled with water. A tap was turned on to fill it up with water at a rate of 9 ℓ/min. Every 20 seconds after the tap was turned on, an iron ball of volume 400 cm3 was added to the tank. How many iron balls of the same volume would there be in the tank when the tank is 100% filled with water?
Percentage of volume of space to be filled
= 100% - 20%
= 80%
Volume of space in the tank
= 80% x 80 x 50 x 48
=
80100 x 80 x 50 x 48
= 153600 cm
3 1 ℓ = 1000 mℓ
9 ℓ = 9 x 1000 = 9000 mℓ
Number of sets of 20 seconds in 1 min
= 60 ÷ 20
= 3
Water flowed in every 20 seconds
= 9000 ÷ 3
= 3000 mℓ
Total volume added for every 20 seconds
= 3000 + 400
= 3400 cm
3 Number of sets of 3400 cm
3= 153600 ÷ 3400
= 45 r 600
After the last iron ball is added, 600 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 45
Answer(s): 45
