A rectangular tank 80 cm by 40 cm by 45 cm was 30% filled with water. A tap was turned on to fill it up with water at a rate of 10 ℓ/min. Every 30 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% - 30%
= 70%
Volume of space in the tank
= 70% x 80 x 40 x 45
=
70100 x 80 x 40 x 45
= 100800 cm
3 1 ℓ = 1000 mℓ
10 ℓ = 10 x 1000 = 10000 mℓ
Number of sets of 30 seconds in 1 min
= 60 ÷ 30
= 2
Water flowed in every 30 seconds
= 10000 ÷ 2
= 5000 mℓ
Total volume added for every 30 seconds
= 5000 + 400
= 5400 cm
3 Number of sets of 5400 cm
3= 100800 ÷ 5400
= 18 r 3600
After the last iron ball is added, 3600 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 18
Answer(s): 18
