The radius of a circle is 10.5 cm. Find its circumference.

Explanation

To find the circumference of a circle when the radius is given, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the given radius**:
The radius (r) of the circle is given as 10.5 cm.

2. **Use the formula for circumference**:
The formula for the circumference (C) of a circle is:
\[ C = 2 \pi r \]
where \(\pi\) (pi) is approximately \( \frac{22}{7} \) or \( 3.14 \).

3. **Substitute the radius into the formula**:
Substitute \( r = 10.5 \) cm into the formula:
\[ C = 2 \times \pi \times 10.5 \]

4. **Use the approximate value of pi**:
We can use \( \pi \approx \frac{22}{7} \) for calculation:
\[ C = 2 \times \frac{22}{7} \times 10.5 \]

5. **Calculate the multiplication**:
First, calculate \( 2 \times \frac{22}{7} \):
\[ 2 \times \frac{22}{7} = \frac{44}{7} \]
Now multiply this by 10.5:
\[ C = \frac{44}{7} \times 10.5 \]

6. **Convert 10.5 to a fraction**:
We can express 10.5 as \( \frac{105}{10} \) or \( \frac{21}{2} \):
\[ C = \frac{44}{7} \times \frac{21}{2} \]

7. **Multiply the fractions**:
Multiply the numerators and denominators:
\[ C = \frac{44 \times 21}{7 \times 2} = \frac{924}{14} \]

8. **Simplify the fraction**:
Divide both the numerator and denominator by 14:
\[ C = 66 \text{ cm} \]

### Final Answer:
The circumference of the circle is **66 cm**.

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