An empty tank measures 50 cm by 20 cm by 45 cm. 3 wooden cubes each of edge 10 cm, are placed in the tank. The tank is then filled with water flowing from a tap at a rate of 7 ℓ per minute.

1. How long will it take to fill up the tank? Express your answer in min.
2. What will be the depth of the water in the tank after 3 wooden cubes are removed?

(a)
Volume of the tank
= 50 x 20 x 45
= 45000 cm³

Volume of 1 cube
= 10 x 10 x 10
= 1000 cm³

Volume of 3 cubes
= 3 x 1000 
= 3000 cm³

Volume of water needed to fill the tank
= 45000 - 3000
= 42000 cm³

1 ℓ = 1000 cm³
 7 ℓ = 7000 cm³
 
Time taken to fill the tank
= 42000 ÷ 7000
= 6 min

(b)
Volume of 3 cubes
= 3 x 1000
= 3000 cm³

Base area of the tank
= 50 x 20
= 1000 cm²

Decrease in the depth of water
= 3000 ÷ 1000
= 3 cm

Depth of water after removing 3 cubes
= 45 - 3
= 42 cm

Answer(s): (a) 6 min; (b) 42 cm