the radius of the circle is reduced from 5 cm to 4 cm then the % change of area .
for 5 cm - > pi * r ^ 2 - - > 3.14 * 5 ^ 2 - > 78.539 for 4 cm - > pi * r ^ 2 - - > 3.14 * 4 ^ 2 - > 50.265 % change - > ( 1 - 50.265 / 78.539 ) * 100 = 36 ie 36 % answer : a
subtract(const_100, multiply(const_100, divide(circle_area(4), circle_area(5))))