Question: The areas of two similar octagons are $4$ m² and $25$ m². What is the scale factor of their side lengths?
1. **State the problem:** We have two similar octagons with areas $4$ m² and $25$ m². We need to find the scale factor of their side lengths.
2. **Recall the formula:** For similar figures, the ratio of their areas is equal to the square of the ratio of their corresponding side lengths. If $k$ is the scale factor of side lengths, then:
$$\frac{\text{Area}_1}{\text{Area}_2} = k^2$$
3. **Apply the given values:**
$$\frac{4}{25} = k^2$$
4. **Solve for $k$:**
$$k = \sqrt{\frac{4}{25}} = \frac{\sqrt{4}}{\sqrt{25}} = \frac{2}{5}$$
5. **Interpretation:** The scale factor of the side lengths is $\frac{2}{5}$ or $0.4$.
This means each side length of the smaller octagon is $0.4$ times the corresponding side length of the larger octagon.