8. Both of the shapes shown in the diagram are formed from the same five pieces, a $5 \mathrm{~cm}$ by $10 \mathrm{~cm}$ rectangle, two large quarter circles and two small quarter circles. What is the difference in $\mathrm{cm}$ between their perimeters?
A 2.5
B 5
C 10
D 20
E 30
Solution
D

Both shapes have two large quarter circles and two small quarter circles in their perimeters. Additionally, the first shape has two edges of length $10 \mathrm{~cm}$ and two edges of length $5 \mathrm{~cm}$ in its perimeter, whereas the second shape has only one edge of length $10 \mathrm{~cm}$ in its perimeter. Therefore the difference, in $\mathrm{cm}$, between their perimeters is $10+5+5=20$.