The areas of two similar figures are 20 cm2 and 45 cm2. What is the scale factor of their corresponding sides? What is the ratio of their perimeters?

The scale factor ratio is just the square root of the area ratio...so

sqrt (45/ 20) = sqrt ( 9 * 5) / sqrt(4 *5) = sqrt (9/4) = 3/2 = 3 : 2

Since perimeter is a linear measure, the perimeter ratio is the same 3 : 2