This problem is related to reality. Although the physical roof caving is cylindrical, it only has a circular top surface π 10? Without a bottom surface, the side surface can be unfolded into a rectangle with a length of 20π and a width of 20; The brim is hollow, which is equivalent to the outer circle MINUS the inner circle. The brim width of 20cm indicates that the diameter of the outer circle is 20+20+20, and the inner circle is equal to the roof caving face.

Formula of circular area: πr? R is the radius, which is half the diameter.

Red cloth 20π×20+ 10? π=500π

Kimble 30? π- 10? π=800π

Which is more?

How much more? 800π-500π=?