A storage tank is in the form of a cube. When it is full of water, the volume of the water is

15.625m3. If the present depth of the water is 1.3m, find the volume of water already

used from the tank.

Let each side of the cubical tank measures a m.

Volume of  water when the tank is full =  15.625 m³

∴ Capacity of tank = 15.625 m³

⇒ a³ = 15.625 m³

⇒ a = 2.5 m

⇒ Depth of tank = 2.5 m

Depth of water = 1.3 m

∴ Depth of empty tank = 2.5 m - 1.3 m = 1.2 m

Volume of used water = Volume of empty tank = 2.5 m × 2.5 m × 1.2 m = 7.5 m³