Yoshi bought 20 stamps this is five times the number of postcard

The answer is 4 postcards

Step-by-step explanation:

20 stamps five times the number of postcards

5x = 20

x = 20/5

x = 4 postcards

cone

Step-by-step explanation:

If in the image you can see that the vertex with the angle of 90° is in the (0,0), then, looking at only the changes in the other vertex, we have.

Before the rotation, we have one vertex in the x = 0 line, and other vertex in the y = 0 line.

After the rotation, the vertex in the y = 0 line will draw a circle, while the point in x= 0 will not do anything (because the point is colinear to the axis of rotation).

Then our figure has a circular base and ends on a point, connecting those figures we can se that the figure is a cone.