How do you find a scale factor of a perimeter? - Answers

Often when working a problem with a scale factor, you are given two similar shapes, and a missing side. For example, you could be given a rectangle with sides A: 3 units and side B: 9 units. Then, you are given another similar rectangle, with side A: 6 units and side B: unknown. To solve this problem, you can simply create a proportion, known in this case as a scale factor. Similar to using a map to predict travel times on a road trip, you can simply create a proportion, in this case, 6:3, which simplifies to 2:1. In this case, the scale factor is 2, so the length of a similar side in the 1st shape is multiplied by 2 to get the length of the same side in the other (2nd) shape. Knowing this side is 9 in the first, and the scale factor is two, we know that the similar side in the 2nd shape is going to be 9 x 2 = 18 units long.