Question

Find the circumference of a circle whose radius is 21cm. (use pi: 22/7)

Answer 1

The formula to find the circumference \( C \) of a circle is given by:

\[
C = 2 \pi r
\]

where \( r \) is the radius of the circle. Given that the radius \( r \) is 21 cm and using \( \pi \) as \( \frac{22}{7} \), we can substitute these values into the formula:

\[
C = 2 \times \frac{22}{7} \times 21
\]

Now, let's calculate it step-by-step:

1. Multiply \( 2 \) and \( 21 \):

\[
2 \times 21 = 42
\]

2. Now substitute that back into the circumference equation:

\[
C = \frac{22}{7} \times 42
\]

3. To multiply \( \frac{22}{7} \) by \( 42 \), we can perform the multiplication:

\[
C = \frac{22 \times 42}{7}
\]

Now calculate \( 22 \times 42 \):

\[
22 \times 42 = 924
\]

4. Now divide \( 924 \) by \( 7 \):

\[
C = \frac{924}{7} = 132
\]

Thus, the circumference of the circle is:

\[
\boxed{132 \text{ cm}}
\]