Practice!

Sample Problem

You have a rectangular aquarium, whose bottom face is a 60 cm × 60 cm square. You put another iron box, which has height 12 cm and a square bottom face of side length 15 cm, into the aquarium. Now, you fill the aquarium 20 cm high with water. After you take out the iron box, what is the depth of the water?

  cm

Solution

The aquarium has a volume of 60 × 60 × 20 = 72000 cm3 of water. However, we need to subtract out the iron that is in the water but not water. This iron has a volume of 15 × 15 × 12 = 2700 cm3. Thus, the actual volume of water is 72000 - 2700 = 69300 cm3. Thus, after the iron box is gone, the depth of the water × 60 × 60 = 67500, so the depth of the water is 69300 ÷ 3600 = 19.25 cm.