A rectangular tank 120 cm by 60 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 15 seconds after the tap was turned on, an iron ball of volume 300 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 120 x 60 x 45
=
70100 x 120 x 60 x 45
= 226800 cm
3 1 ℓ = 1000 mℓ
10 ℓ = 10 x 1000 = 10000 mℓ
Number of sets of 15 seconds in 1 min
= 60 ÷ 15
= 4
Water flowed in every 15 seconds
= 10000 ÷ 4
= 2500 mℓ
Total volume added for every 15 seconds
= 2500 + 300
= 2800 cm
3 Number of sets of 2800 cm
3= 226800 ÷ 2800
= 81 r 0
After the last iron ball is added, 0 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 81
Answer(s): 81