Question

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

Answer 1

Answer: B.
`(1)/(5)`

Explanation:

Given: The circumference of a circle changes from (pre-image)20 to 4(image) after a dilation.

Then, the scale factor is given by :-

`\text{Scale factor}=\frac{\text{Circumference of image}}{\text{Circumference of pre-image}}\\\\\Rightarrow\text{Scale factor}=(4)/(20)\\\\\Rightarrow\text{Scale factor}=(1)/(5)`

Hence, the scale factor after dilation =
`(1)/(5)`

Answer 2

The answer is the option B

`(1)/(5)`

Explanation:

we know that

To find the scale factor divide the circumference of the dilated circle by the circumference of the original circle

so

`scale\ factor=(4)/(20)=(1)/(5)`