$△ABC$ is similar to $△DEF$. Length of $AB$ is $12\text{ cm}$ and length of the corresponding side $DE$ is $8\text{ cm}$. What is the ratio of Perimeter of $△ABC$ : Perimeter of $△DEF$?

For any two similar triangles, the ratio of their perimeters is equal to the ratio of their corresponding sides.Given:$△ABC\sim △DEF$$AB=12\text{ cm}$$DE=8\text{ cm}$ Therefore:
$$\frac{\text{Perimeter of }△ABC}{\text{Perimeter of }△DEF}=\frac{AB}{DE}$$
Substituting the given values:
$$\frac{\text{Perimeter of }△ABC}{\text{Perimeter of }△DEF}=\frac{12}{8}=\frac{3}{2}$$
Thus, the ratio is $3:2$.