A rectangular tank 120 cm by 50 cm by 43 cm was 20% filled with water. A tap was turned on to fill it up with water at a rate of 6 ℓ/min. Every 10 seconds after the tap was turned on, an iron ball of volume 500 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 120 x 50 x 43
=
80100 x 120 x 50 x 43
= 206400 cm
3 1 ℓ = 1000 mℓ
6 ℓ = 6 x 1000 = 6000 mℓ
Number of sets of 10 seconds in 1 min
= 60 ÷ 10
= 6
Water flowed in every 10 seconds
= 6000 ÷ 6
= 1000 mℓ
Total volume added for every 10 seconds
= 1000 + 500
= 1500 cm
3 Number of sets of 1500 cm
3= 206400 ÷ 1500
= 137 r 900
After the last iron ball is added, 900 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 137
Answer(s): 137