Answer:
1. 20 half of 20 is 10(new radius),
10^10 = 100
100 x 3.14 = 314
314 divided by 2 = 157
2. 8 x 8 = 64, 64 divided by 2 ( x 1/2) = 32
half of 8 is 4(new radius)
4 ^4 = 16, 16 x 3.14 = 50.24
50.24 divided by 2 = 25.12
25.12 + 32 = 57.12
3. Half of 7 is 3.5(new radius)
Just find the area of a full circle since two semi circles make a full circle.
3.5^2 = 12.25
12.25 x 3.14 = 38.465,
21 x 7 = 147
147 + 38.465 = 185.465
4. Half of 6 is 3(new radius)
3^3 = 9
9 x 3.14 = 28.26, 28.26 divided by 2 = 14.13
11 x 6 = 66, 66 divided by 2 (x 1/2) = 33
14.13 + 33 = 47.13
5. 81 divided by 4 = 20.25
half of 20.25 is 10.125(new radius)
10.125 x 2 x 3.14 = 63.585 rounded = 63.59
