If two figures are similar by a scale factor, then the perimeter of one figure is equal to the perimeter of the other figure multiplied by the scale factor.
Since polygon ABCD and polygon GHIJ are similar, the perimeter of polygon GHIJ is equal to the perimeter of polygon ABCD multiplied by the scale factor. Therefore, to find the unknown perimeter we first need to find the scale factor. The scale factor is the quotient of the two corresponding side lengths.
Scale Factor [0.5em]
GJ/AD substitute ⟶ 2/5
Finally, the perimeter of polygon GHIJ is equal to 21 times 25.
