A rectangular tank 120 cm by 50 cm by 47 cm was 10% filled with water. A tap was turned on to fill it up with water at a rate of 7 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% - 10%
= 90%
Volume of space in the tank
= 90% x 120 x 50 x 47
=
90100 x 120 x 50 x 47
= 253800 cm
3 1 ℓ = 1000 mℓ
7 ℓ = 7 x 1000 = 7000 mℓ
Number of sets of 30 seconds in 1 min
= 60 ÷ 30
= 2
Water flowed in every 30 seconds
= 7000 ÷ 2
= 3500 mℓ
Total volume added for every 30 seconds
= 3500 + 400
= 3900 cm
3 Number of sets of 3900 cm
3= 253800 ÷ 3900
= 65 r 300
After the last iron ball is added, 300 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 65
Answer(s): 65
