## Geometry: Common Core (15th Edition)

The scale factor is $\frac{5}{3}$ or $5:3$.
Similar triangles have congruent angles and proportional sides. In this exercise, we are asked to find the scale factor, so we need to compare corresponding sides in the triangles where values are actually given: $\frac{DF}{HK} = \frac{30}{18}$ Divide the numerator and denominator by their greatest common factor, $6$: $\frac{DF}{HK} = \frac{5}{3}$ The scale factor is $\frac{5}{3}$ or $5:3$.