Question

Suppose the radius of a circle is 1. What is its circumference?

Either enter an exact answer in terms of pi or use 3.14 for pi and enter your answer as a decimal.

Answer 1

C = 2 x 3.14 x 1 (use pi as 3.14)
C = 6.28

Answer 2

The radius x2 is the diameter. The Diameter x $\pi$ is the Circumference. 
So Lets work it out.
the Radius is 1.
1x2=2 right?
So 2xpi
Use pi as 3.14
3.14x2
3.14x2=6.28.
So the Circumference is 6.28.
ANS:6.28