 You can use similar figures to find missing information about one of the figures, when you know the measurements of at least one of the figures and some of the measurements of the other.

 The reason for this is that similar figures have proportional measurements.  Let’s look at an example.

5 m 10 m x 5 m Determine the width, x, of the smaller rectangle, given that the two figures are similar.

 Because the two figures are similar, their dimensions will be proportional.  Another way to think of it is that the width of the larger rectangle divided by its length will have the same ratio as the width of the smaller triangle divided by its length.

Using the fact that the measurements are proportional for similar figures can help you solve for the missing measurement. Cross-multiply. Solve for x. The width of the smaller rectangle.

 This method will work for any two similar figures so long as you can compare the ratio of different measurements in one figure to the ratio of corresponding measurements in the other figure and know at least three of the measurements.