Cow Grazing

(A true story) A rancher wrote a local university to pose this problem: "On my land is a water tower that has a diameter of 20 feet. To it, I have tied a cow with a rope that is 20 feet long. What is the area of grass that the cow can graze?''

Using a compass, draw a picture on graph paper of the water tower and the cow's grazing area. Make sure the grazing area is physically possible for the cow to reach.

Now estimate or compute the area that the cow can graze. Explain your method of estimating the area.