Find the radius of a circle whose circumference is 31.4 centimeters. approximate π as 3.14.

The circumference of every circle is   (pi) times (diameter).

The diameter is (2 x radius), so we can write

                  Circumference = (pi) x (2 x radius) .

The question gives us the circumference, and the number to use for (pi).
I shall now pluggum in:

                  (31.4 cm)  =  (3.14) x (2 x radius)

Divide each side by  3.14:       (31.4 cm)/(3.14)  =  2 x radius

Divide each side by 2 :            (31.4 cm) / (2 x 3.14)  =  radius

                                                             5 cm  =  radius