Math CentralQuandaries & Queries


Question from sara, a parent:

a rectangular tank 30 cm long and 20 cm wide is filled with water to a depth of 8 cm. When a stone was put in, the water level rose to 11 cm. Find the volume of the stone. (Assume that the stone is completely under water.)

Hi Sara,

When the stone is placed in the water it displaces some of the water. If the stone doesn't absorb any of the water then the displaced water has a volume equal to the volume of the stone. The displaced water causes the water level to rise, in your case it rises 11 - 8 = 3 cm. Hence the volume of the stone is equal to the volume of the displaced water which is a slab of water 30 cm by 20 cm by 3 cm.

I hope this helps,

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