Practice worksheet for finding the circumference of circles using diameter and radius measurements.

Let's solve each problem step by step using the formula for the circumference of a circle:

$$
C = \pi d \quad \text{or} \quad C = 2\pi r
$$

We'll use $ \pi \approx 3.14 $ unless otherwise specified.

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Problem 1: Circle with diameter = 5 m

Given: $ d = 5 $ m
Use: $ C = \pi d $

$$
C = \pi \times 5 = 3.14 \times 5 = 15.7 \, \text{m}
$$

✔ Answer: $ C = 15.7 $ m

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Problem 2: Circle with diameter = 12 cm

Given: $ d = 12 $ cm
Use: $ C = \pi d $

$$
C = \pi \times 12 = 3.14 \times 12 = 37.68 \, \text{cm}
$$

✔ Answer: $ C = 37.68 $ cm

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Problem 3: Circle with radius = 7 m

Given: $ r = 7 $ m
Use: $ C = 2\pi r $

$$
C = 2 \times \pi \times 7 = 2 \times 3.14 \times 7 = 43.96 \, \text{m}
$$

✔ Answer: $ C = 43.96 $ m

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Problem 4: Circle with diameter = 32 m

Given: $ d = 32 $ m
Use: $ C = \pi d $

$$
C = \pi \times 32 = 3.14 \times 32 = 100.48 \, \text{m}
$$

✔ Answer: $ C = 100.48 $ m

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Problem 5: Circle with radius = 18 mm

Given: $ r = 18 $ mm
Use: $ C = 2\pi r $

$$
C = 2 \times \pi \times 18 = 2 \times 3.14 \times 18 = 113.04 \, \text{mm}
$$

✔ Answer: $ C = 113.04 $ mm

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Problem 6: Circle with diameter = 21 cm

Given: $ d = 21 $ cm
Use: $ C = \pi d $

$$
C = \pi \times 21 = 3.14 \times 21 = 65.94 \, \text{cm}
$$

✔ Answer: $ C = 65.94 $ cm

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Bonus Question:

> If the circumference of a circle is 42 m, what is the diameter? What is the radius?

We know:
$$
C = \pi d \Rightarrow d = \frac{C}{\pi}
$$

So:
$$
d = \frac{42}{3.14} \approx 13.375 \, \text{m}
$$

Now, radius $ r = \frac{d}{2} = \frac{13.375}{2} \approx 6.6875 $ m

Or directly:
$$
r = \frac{C}{2\pi} = \frac{42}{2 \times 3.14} = \frac{42}{6.28} \approx 6.6875 \, \text{m}
$$

✔ Answer:
- $ D = 13.375 $ m
- $ R = 6.6875 $ m

(You can round to 2 decimal places if needed: $ D \approx 13.38 $ m, $ R \approx 6.69 $ m)

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✔ Final Answers Table:

| Problem | Answer (with units) |
|--------|----------------------|
| 1) C = π × 5 | 15.7 m |
| 2) C = π × 12 | 37.68 cm |
| 3) C = 2π × 7 | 43.96 m |
| 4) C = π × 32 | 100.48 m |
| 5) C = 2π × 18 | 113.04 mm |
| 6) C = π × 21 | 65.94 cm |
| D = ? | 13.375 m |
| R = ? | 6.6875 m |

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📝 Note: Always keep track of units and avoid extra spaces. Use $ \pi \approx 3.14 $ unless told otherwise.

Let me know if you want it formatted for a worksheet!