Find the area of a circle whose diameter is :
(i) 18.2 cm
(ii) 30.8 cm

Answer

To find the area of a circle given its diameter, we can follow these steps:

### Step-by-Step Solution:

**(i) For the diameter of 18.2 cm:**

1. **Calculate the radius:**
\[ \text{Radius} (r) = \frac{\text{Diameter}}{2} = \frac{18.2 \text{ cm}}{2} = 9.1 \text{ cm} \]

2. **Use the area formula for a circle:**
\[ \text{Area} = \pi r^2 \]
Here, we will use \(\pi \approx \frac{22}{7}\).

3. **Substitute the radius into the area formula:**
\[ \text{Area} = \frac{22}{7} \times (9.1)^2 \]

4. **Calculate \(9.1^2\):**
\[ 9.1^2 = 82.81 \]

5. **Now substitute back to find the area:**
\[ \text{Area} = \frac{22}{7} \times 82.81 \]

6. **Calculate \(\frac{22 \times 82.81}{7}\):**
\[ \text{Area} = \frac{1821.82}{7} \approx 260.26 \text{ cm}^2 \]

**(ii) For the diameter of 30.8 cm:**

1. **Calculate the radius:**
\[ \text{Radius} (r) = \frac{\text{Diameter}}{2} = \frac{30.8 \text{ cm}}{2} = 15.4 \text{ cm} \]

2. **Use the area formula for a circle:**
\[ \text{Area} = \pi r^2 \]
Again, we will use \(\pi \approx \frac{22}{7}\).

3. **Substitute the radius into the area formula:**
\[ \text{Area} = \frac{22}{7} \times (15.4)^2 \]

4. **Calculate \(15.4^2\):**
\[ 15.4^2 = 237.16 \]

5. **Now substitute back to find the area:**
\[ \text{Area} = \frac{22}{7} \times 237.16 \]

6. **Calculate \(\frac{22 \times 237.16}{7}\):**
\[ \text{Area} = \frac{5217.52}{7} \approx 745.36 \text{ cm}^2 \]

### Final Answers:
- Area of the circle with diameter 18.2 cm is approximately **260.26 cm²**.
- Area of the circle with diameter 30.8 cm is approximately **745.36 cm²**.