Krishna
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Step 1: Measure or record the diameter.


Step 2: Divide the diameter in half.

            NOTE: Remember that the diameter is equal to double the radius.

                              d = 2r

                             r = \frac{d}{2} = \frac{20}{2}

Step 3: Substitute the radius in the area of the circle formula.

            NOTE: Area of the circle = \pi r^2


Step 4: Square the radius and multiply by \pi. 

          EXAMPLE: Radius r = 14, then

                                 A =   \pi 14^2

                          A =   \frac{22}{7} * 196    ( since  \pi = \frac{22}{7} =3.14)

                             A    = 615.44 cm^2