## Algebra 1: Common Core (15th Edition)

The airplane is a model, so the two models are similar shapes. This means that all of the sides are proportional. We will call x the side that we want to find (the length of the model). Thus, we set up the equation: $15/25=x/20$. We see that the variable only appears in the numerator of the fractions, so we know that the Multiplication Property of Equality will work well. We multiply both sides of the equation by 20 to obtain that x=12. The length of the model is 12 inches.