We are told that two similar parallelograms have areas of 20cm^2 and 3.2cm^2.
If the scale factor of two similar figures is ab, then the ratio of its areas is a^2b^2. Since we know the areas, we can write a proportion using the ratio of the areas.
a^2/b^2=20/3.2
Finally, we can take square roots on both sides of the above equation to find the value of ab. Keep in mind that we will only keep the principal roots because in the context of the exercise only positive numbers make sense.
