Question

If the radius of a circle is doubled in length, the circumference of the circle is
A.
halved

B.
doubled

C.
tripled

Answer 1

If you start with
C = 2 π r

Then you double the radius.
C ' = 2 π (2r )

what happens to the new circumference C '

Answer 2

C ' = 2 π (2r ) = 2 * 2π r = 2 * C

Answer 3

thankyou @perl