Title: There is a hat. The top of the hat is cylindrical and made of cloth. The brim part is a ring, which is also the same cloth. It is known that the radius, height and brim width of a hat are all one meter. So how many square decimetres of cloth does it take to make this hat?

Solution: There is a known hat, the top of which is cylindrical and made of cloth. The brim part is a ring, which is also the same cloth. It is known that the radius, height and width of the brim are 1 decimeter.

The fabric area needed to make this hat = hat top area+hat brim area.

=(3. 14× 1? +3. 14× 1×2× 1)+3. 14×[( 1+ 1)? - 1? ]

=3. 14+6.28+3. 14×(2? - 1)

=9.42+3. 14×(4- 1)

=9.42+3. 14×3

=9.42+9.42

= 18.84 square decimeter

To make this hat, you should use at least 18.84 square decimeters of fabric.