## 73. Math Puzzle $6 / 71$

From a sheet of metal in the shape of a regular heptagon, whose sides are at a distance of $15 \mathrm{~cm}$ from the center, a $1 \mathrm{~cm}$ wide strip is cut off all around. What percentage of the material is wasted as a result?
After cutting off the strip, a similar heptagon is formed. For the areas $A_{\text {before }}$ and $A_{\text {after }}$, the following applies

$$
\frac{A_{\text {after }}}{A_{\text {before }}}=\left(\frac{14}{15}\right)^{2}=\frac{196}{225}
$$

with a relative reduction of $\frac{29}{225} \approx 12.9 \%$.