Question

The diameter of a circle is 21cm find the perimeter of the circle

Answer 1

circumference of a circle

$= \pi \times radius \\ \\ = \pi \times half \: of \: diamter \\ \\ = \\ = 1.4 \times 6 \\ = 84$

answer is 84

Answer 2

Here's what you had asked for:

Circumference of circle= 2$\pi$r

                                      = 2× $\frac{22}{7}$× $\frac{21}{2}$ (Simplification in the pic)

                                      = 2× 11× 3

                                      = 66cm