Answer:
In two similar geometric figures, the scale factor is the ratio of their corresponding sides, dividing the two corresponding lengths of the sides will gives the ratio, for example
What is the scale factor between 4 cm and 10 cm ?
4 and 10 are divisible by 2
Length A : 4 ÷ 2 = 2
Length B : 10 ÷ 2 = 5
so the scale factor from A to B is 2:5