Final answer:
To determine the length of the unknown side, set up a proportion using the scale factor and cross multiply to solve for it.
Step-by-step explanation:
In order for two figures to be similar, the corresponding sides must be proportional. To determine the length of the unknown side, we can set up a proportion using the scale factor.
For example, if the scale factor is 1:20, then the ratio of the length of the unknown side to the length of the actual side would be 1/20. To find the length of the unknown side, we can cross multiply and solve for it.
Scale length / Actual length = 1 / 20
Scale length = (Actual length) / 20