Water flows into a tank at the rate of 30 ℓ per minute. After 20 min, the tap is turned off and the tank is 0.8 filled with water.

1. How much more water is needed to fill it to the brim?
2. The water in the tank is then poured into containers each 1.2 m long, 0.1 m wide and 20 cm high. What is the minimum number of containers needed?

(a)
0.8 =  ⁴₅

Let 5 u be the total volume of water when the tank is completely filled.

Volume of water in the tank
= 30 x 20
= 600 ℓ

4 u = 600

1 u = 600 ÷ 4 = 150

Volume of water to fill the tank to the brim
= 5 u - 4 u
= 1 u
= 1 x 150
= 150 ℓ

(b)
1 m = 100 cm
1.2 m = 120 cm
0.1 m = 10 cm

Volume of each container
= 120 x 10 x 20
= 24000 cm³

Volume of water in the tank = 600 ℓ

1 ℓ = 1000 mℓ
600 ℓ = 600000 mℓ

Number of containers needed
= 600000 ÷ 24000
= 25 r 0

Minimum number of containers needed
= 25 + 1 
= 26

Answer(s): (a) 150 ℓ; (b) 26