Scaling figures and the scale ratio - 7th grade math
When a figure is enlarged or shrank proportionally, or when two figures are similar, the scale ratio is the ratio of one side of the figure to the corresponding side in the other. When the scale ratio is given, we can solve an unknown side. Or, if a set of corresponding sides is given, we can write a proportion to solve for the unknown side.
See also
How to calculate distances on the map or in reality using the map scale
Math Mammoth Grade 7 curriculum (pre-algebra)