Question

If the radius of a circle is decreased by 20%, find the percentage decreasearca:A 36%32%C. 21%D. 42%​

Answer 1

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%

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