Do you mean Pi (π)? If not here:
The diameter of a circle is 5 dm, find the circumference.
πd(diameter) or 2π(3.14)r(radius)
3.14(π) x 2=6.28 x 2.5 (radius= divide by 2,diameter=don't divide ) = 15.71 dm or
3.14 x 5 = 5.71 dm
It's pretty easy, actually, just be alert if the questions says diameter or radius
Hope this helped you