<u>ANSWER:
</u>
After changing the side lengths of the triangle are decreased by scale factor of 3, the perimeter of triangle also decreased by 3
<u>SOLUTION:</u>
Given, the side lengths of a triangle are decreased by a scale factor of 3.
Let the side lengths of the given triangle be a, b, c.
After the side lengths are decreased by a scale factor of 3.
Now, the side lengths will become 
Before changing the side lengths, perimeter of the triangle is p = a + b + c.
After changing the side lengths, perimeter of the triangle is 


So, the perimeter is also decreased by the scale factor of 3.
Hence, after changing the side lengths of the triangle are decreased by scale factor of 3, the perimeter of triangle also decreased by 3.