【Solution】Solution: The radius of the large circle is: $20 \div 2=10$ (cm),
The radius of the small circle is: $10 \div 2=5$ (cm),
$$
\begin{array}{l}
3.14 \times 10^{2}-2 \times 3.14 \times 5^{2}, \\
=314-175, \\
=157 \text { (square cm), }
\end{array}
$$

Answer: The area of the shaded part is 157 square cm.
9. In the handicraft class, Xiaohong cut out a windmill pattern (the blank part) from a circular paper with a diameter of $20 \mathrm{~cm}$ as shown in the figure. The area of the paper that was cut off (the shaded part) is $\qquad$ $\mathrm{cm}^{2}$. ( $\pi$ is taken as 3.14)