jhonnybravo wrote:

a certain cloth with a diameter of 20 inches is placed in a circular tray with a diameter of 24 inches . What fraction of trays surface is not covered by a cloth?

1) 1/6

2)1/5

3)11/36

4)25/36

5)5/6

I have a silly question but I need some clarification why does it have to be the ratio of the area's and not circumference?

The questions asks us to find the surface which is not covered by the cloth i.e., area of the surface not covered.

Where as circumference is the length along the edge of the circle,

2*pi*r implies the length of the curve

pi*r^2 implies area enclosed by that curve..hence Area of the circle is considered for this problem

Area of the tray=pi* r^2, where r=12

=>pi*144

Area of the cloth=pi*100

Surface not covered by the cloth=pi*144-pi*100=Pi*44

fraction of trays surface is not covered by a cloth= Pi*44/total area of the tray

=>Pi*44/Pi*144

=>11/36

Hope its clear