A rectangular tank 110 cm by 50 cm by 42 cm was 30% filled with water. A tap was turned on to fill it up with water at a rate of 7 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 110 x 50 x 42
=
70100 x 110 x 50 x 42
= 161700 cm
3 1 ℓ = 1000 mℓ
7 ℓ = 7 x 1000 = 7000 mℓ
Number of sets of 15 seconds in 1 min
= 60 ÷ 15
= 4
Water flowed in every 15 seconds
= 7000 ÷ 4
= 1750 mℓ
Total volume added for every 15 seconds
= 1750 + 300
= 2050 cm
3 Number of sets of 2050 cm
3= 161700 ÷ 2050
= 78 r 1800
After the last iron ball is added, 1800 cm
3 of water will flow into the tank so that the tank is 100% filled with water.
Number of iron balls added = 78
Answer(s): 78
