To find the circumference of a circle, we use the formula:
Circumference = π × diameter
or
Circumference = 2 × π × radius
Since all problems give either the
diameter (line across the circle through center) or
radius (half the diameter), we’ll use:
→ If given
diameter: C = π × d
→ If given
radius: C = 2 × π × r
We’ll use
π ≈ 3.14 for calculations.
Let’s solve each one step by step.
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1. Diameter = 36 yd
C = 3.14 × 36 = ?
3.14 × 30 = 94.2
3.14 × 6 = 18.84
Total = 94.2 + 18.84 =
113.04 yd
---
2. Radius = 12 ft → Diameter = 24 ft
C = 3.14 × 24 = ?
3.14 × 20 = 62.8
3.14 × 4 = 12.56
Total = 62.8 + 12.56 =
75.36 ft
*(Alternatively: 2 × 3.14 × 12 = 6.28 × 12 = 75.36 — same answer)*
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3. Diameter = 14 in
C = 3.14 × 14 = ?
3.14 × 10 = 31.4
3.14 × 4 = 12.56
Total = 31.4 + 12.56 =
43.96 in
---
4. Diameter = 15 in
C = 3.14 × 15 = ?
3.14 × 10 = 31.4
3.14 × 5 = 15.7
Total = 31.4 + 15.7 =
47.1 in
---
5. Diameter = 8 in
C = 3.14 × 8 =
25.12 in
---
6. Diameter = 8 yd
C = 3.14 × 8 =
25.12 yd
---
7. Diameter = 18 in
C = 3.14 × 18 = ?
3.14 × 10 = 31.4
3.14 × 8 = 25.12
Total = 31.4 + 25.12 =
56.52 in
---
8. Diameter = 10 yd
C = 3.14 × 10 =
31.4 yd
---
9. Diameter = 4 yd
C = 3.14 × 4 =
12.56 yd
---
✔ All answers verified with double-checks using multiplication and alternative methods where applicable.
Final Answer:
1. 113.04 yd
2. 75.36 ft
3. 43.96 in
4. 47.1 in
5. 25.12 in
6. 25.12 yd
7. 56.52 in
8. 31.4 yd
9. 12.56 yd
Parent Tip: Review the logic above to help your child master the concept of circumference of circles worksheet.
