The circumference of a circle changes from 20 to 4 after a dilation. What was the scale factor of the dilation?

A. 1/25
B. 1/5
C. 5
D. 25

B. 1/5

To find the scale factor of a dilation, you need to divide the new measurement by the original measurement. In this case, you need to divide the new circumference (4) by the original circumference (20).

So, the scale factor (k) is calculated as:
k = new circumference / original circumference

k = 4 / 20 = 1/5

Therefore, the scale factor of the dilation is 1/5.

The answer is B.

um, try 4/20