Let's solve each problem step by step using the formula for the
area of a circle:
$$
\text{Area} = \pi r^2
$$
Where:
- $ r $ is the radius of the circle
- $ \pi \approx 3.14 $ (we'll use this approximation unless otherwise specified)
---
Problem 1: Example (Already Solved)
- Radius = 7 cm
- Area = $ \pi \times 7^2 = \pi \times 49 \approx 153.9 \, \text{cm}^2 $
✔ Correct!
---
Problem 2: Radius = 12 cm
$$
\text{Area} = \pi \times 12^2 = \pi \times 144
$$
Now calculate:
$$
\pi \times 144 \approx 3.14 \times 144 = 452.16 \, \text{cm}^2
$$
Answer:
- Area of circle = $ \pi \times 144 $
- Area of circle =
452.2 cm² (rounded to one decimal place)
---
Problem 3: Radius = 8 cm
$$
\text{Area} = \pi \times 8^2 = \pi \times 64
$$
Calculate:
$$
3.14 \times 64 = 200.96 \, \text{cm}^2
$$
Answer:
- Area of circle = $ \pi \times 64 $
- Area of circle =
201.0 cm² (rounded to one decimal place)
---
Problem 4: Radius = 10 cm
$$
\text{Area} = \pi \times 10^2 = \pi \times 100
$$
Calculate:
$$
3.14 \times 100 = 314 \, \text{cm}^2
$$
Answer:
- Area of circle = $ \pi \times 100 $
- Area of circle =
314.0 cm²
---
Problem 5: Radius = 5 cm
$$
\text{Area} = \pi \times 5^2 = \pi \times 25
$$
Calculate:
$$
3.14 \times 25 = 78.5 \, \text{cm}^2
$$
Answer:
- Area of circle = $ \pi \times 25 $
- Area of circle =
78.5 cm²
---
Problem 6: Radius = 4 cm
$$
\text{Area} = \pi \times 4^2 = \pi \times 16
$$
Calculate:
$$
3.14 \times 16 = 50.24 \, \text{cm}^2
$$
Answer:
- Area of circle = $ \pi \times 16 $
- Area of circle =
50.2 cm² (rounded to one decimal place)
---
✔ Final Answers:
| Problem | Area Expression | Area (cm²) |
|--------|-------------------------|----------------|
| 2 | $ \pi \times 144 $ |
452.2 |
| 3 | $ \pi \times 64 $ |
201.0 |
| 4 | $ \pi \times 100 $ |
314.0 |
| 5 | $ \pi \times 25 $ |
78.5 |
| 6 | $ \pi \times 16 $ |
50.2 |
---
🔍 Summary:
You always use the formula:
$$
\text{Area} = \pi r^2
$$
Just square the radius and multiply by $ \pi $. Use $ \pi \approx 3.14 $ for calculations.
Let me know if you'd like to see how to do it with more precise values of $ \pi $!
Parent Tip: Review the logic above to help your child master the concept of math worksheet grade 7.
