Why is the wafer area pi*r^2/4 instead of pi*r^2?

[onqun]

Hello guys, I have an upcoming test. When I was doing a question about finding the area of the wafer. it is circular. In the solution manual it says pi*r^2 / 4 . I do not understand where 1/4 comes from. Since it is circular , I assumed the pi*r^2 would be fine.

 

[dlgoff]

Usable area? I could see a little waste but not that much.

 

[onqun]

it just says compare the areas of wafers for the gven diameters .

 

[onqun]

nevermind i just found d=2r ;lol sorry