Posted by **Saw Phone Thet** on Tuesday, September 28, 2010 at 8:16pm.

In similar triangles ABC and DEF, corresponding sides AB and DE equal 15 and 12, respectively. If the perimeter of triangle ABC=40, what is the perimeter of triangle DEF

- geometry -
**Reiny**, Tuesday, September 28, 2010 at 8:48pm
because of similar triangles, each side of triangle DEF is 12/15 or 4/5 as long as the corresponding sides of ABC

in first

a+b+15 = 40

a+b = 25

in DEF

perimeter = e+d + 12

= (4/5)b + (4/5)a + 12

= (4/5)(b+a) + 12

= (4/5)(25) + 12

= 32

Or

by just "common sense" if each side is 4/5 of the old triangle then the new perimeter is (4/5) of 40 or 32

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