Sixth Grade Challenging Math

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6-81)   Answer

                          22.86 inches

Solution: The volume of the water in the tank is 10 * 40 * 40 cubic inches. The area of the base of the cubic shaped metal is 30 * 30 = 900 square inches. After the metal piece is placed in the fish tank, the area of the base is reduced to 40² - 30² square inches. The  volume of water remains unchanged.  Therefore, the height of the water level is: (10 * 40 * 40)/(40² - 30²) = 22.86 inches

* means multiply