SOLUTION: Two similar polygons have a scale factor of 3:5. The parameter of the larger polygon is 120 feet. Find the parameter of the smaller polygon. <--- question. Ok, so my teacher didn

Question 948921: Two similar polygons have a scale factor of 3:5. The parameter of the larger polygon is 120 feet. Find the parameter of the smaller polygon. <--- question.
Ok, so my teacher didn't really make it clear what I was supposed to do on this problem and he isn't answering any of my emails. The only thing he really taught on this lesson was the toothbrush method and cross multiplying stuff. I'm like really confused and would be grateful for any help I could get...
Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
if you mean the perimeter, then the perimeters is in the same ratio as any side of the polygon.
the scale factor is 3:5.
this means:
if you let x = the perimeter of the smaller polygon, and you let y = the perimeter of the larger polygon, then you get the ratio of x/y = 3/5.
you can solve for either x or y, depending on the situation.
you are given that the perimeter of the larger polygon is equal to 120.
this means that y = 120 because y represents the perimeter of the larger polygon.
you get x/y = 3/5 becomes x/120 = 3/5 because y is equal to 120.
you solve for x to get x = 3/5 * 120 which results in y = 72
the perimeter of the smaller polygon is 72.
to test if this is correct, replace x with 72 and y with 120 and you get:
x/y = 3/5 becomes 72/120 = 3/5
here's where you want to cross multiply to see if the ratios are the same.
you get 72 * 5 = 120 * 3 which results in 360 = 360 which are equal to each other which says that the ratios are the same.
the perimeter of the smaller polygon is equal to 72 feet if the perimeter of the larger polygon is equal to 120 feet.

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