Solution: cut into two identical semi-cylinders along the bottom diameter, and the surface area will increase by 40 square decimeters. The area of the rectangular cut should be 20 square decimeters, the length is 1 meter, and the base diameter is 2 decimeters through the area formula. Then according to the volume formula, the bottom area (with a diameter of 2 decimeters) is multiplied by the height (1 meter, that is, 10 decimeter) to get the answer.