SOLUTION: If a circle with a radius of 10 has its radius decreased by 2 , by what percent is the area decreased? A. 20% B. 25%C. 36% D. 40% E. none

Algebra ->  Circles -> SOLUTION: If a circle with a radius of 10 has its radius decreased by 2 , by what percent is the area decreased? A. 20% B. 25%C. 36% D. 40% E. none      Log On


   

Question 369568: If a circle with a radius of 10 has its radius decreased by 2 , by what
percent is the area decreased?
A. 20% B. 25%C. 36% D. 40% E. none
Found 2 solutions by Alan3354, nerdybill:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Oooh, decrease.
Area is a function of the square of the radius.
0.8*r --> 0.8^2*area
--> 0.64*area = 36% decrease


Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
If a circle with a radius of 10 has its radius decreased by 2 , by what
percent is the area decreased?
A. 20% B. 25%C. 36% D. 40% E. none
.
Since area of any circle:
(pi)r^2
.
10 inch radius circle:
(pi)10^2 = 100(pi)
.
8 inch radius circle:
(pi)8^2 = 64(pi)
.
Decrease:
100(pi) - 64(pi) = 36(pi)
.
Percent of decrease:
[36(pi)]/[100(pi)] * 100
36/100 * 100
36%