1 ... Make a rectangle with the largest surface area with four square wooden blocks with side length of 1dm, and its surface area is (18). If you make a rectangle with the smallest surface area, its surface area is (10).

2. If a log with a radius of 2dm and a length of 1m is evenly cut into two sections, the surface area will increase by (12.56) square decimeter.

3. An annular iron sheet with an outer diameter of 5 cm and an inner diameter of 6 cm. The area of this circular iron sheet is (50.24) square centimeters.