Answer:
7.065
Explanation:
There are two ways to do this:
(Note: area = pi * r^2)
Method 1:
Diameter of A = 4, so radius = 4/2 = 2
Area of A = 3.14 * 2^2 = 12.56
Diameter of B = 5, so radius = 5/2 = 2.5
Area of B = 3.14 * 2.5^2 = 19.625
Difference in area = 19.625 - 12.56 = 7.065
Method 2:
First find out how much larger the diameter of B is than A, so 5/4 = 1.25.
What this means is if you take the diameter of A and multiply it by 1.25, you get the diameter of B.
When dealing with area, the area of B will be 1.25^2 times bigger than A.
Area of A = 3.14 * 2^2 = 12.56
So area B = 12.56 * 1.25^2 = 19.625
Difference = 19.625 - 12.56 = 7.065