Question 274809
If the radius of a circular region were decreased by 20 percent, the area of the circular region would decrease by what percent? 

If R is the original radius then the area of the circle is pi*R^2

If we decrease the radius by 20% the new radius is .8*R so the new area is:
pi*(.8*R)^2 = pi*(.64*R^2).

Compute the percent of the new to the old:


(pi*.64R^2)/(pi*R^2) = .64

The decrease then is 100 - 64 = 36%