To find the circumference of a circle, we use the formula:
Circumference = π × diameter
or
Circumference = 2 × π × radius
Since all the problems give us either the
diameter (a line across the circle through the center) or the
radius (half the diameter), we can use the right formula.
We’ll use
π ≈ 3.14 for these calculations.
Let’s go one by one.
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Problem 1: Diameter = 36 yd
Circumference = π × diameter = 3.14 × 36
→ 3.14 × 36 = let's calculate:
3 × 36 = 108
0.14 × 36 = 5.04
Total = 108 + 5.04 =
113.04 yd
✔ Check: 3.14 × 36 = 113.04 → correct.
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Problem 2: Diameter = 12 ft
Circumference = 3.14 × 12
→ 3 × 12 = 36
0.14 × 12 = 1.68
Total = 36 + 1.68 =
37.68 ft
✔ Check: 3.14 × 12 = 37.68 → correct.
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Problem 3: Diameter = 14 in
Circumference = 3.14 × 14
→ 3 × 14 = 42
0.14 × 14 = 1.96
Total = 42 + 1.96 =
43.96 in
✔ Check: 3.14 × 14 = 43.96 → correct.
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Problem 4: Radius = 15 in → so diameter = 15 × 2 = 30 in
Circumference = 3.14 × 30
→ 3 × 30 = 90
0.14 × 30 = 4.2
Total = 90 + 4.2 =
94.2 in
✔ Check: 3.14 × 30 = 94.2 → correct.
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Problem 5: Diameter = 8 in
Circumference = 3.14 × 8
→ 3 × 8 = 24
0.14 × 8 = 1.12
Total = 24 + 1.12 =
25.12 in
✔ Check: 3.14 × 8 = 25.12 → correct.
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Problem 6: Diameter = 8 yd
Same as problem 5, just different unit.
Circumference = 3.14 × 8 =
25.12 yd
✔ Correct.
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Problem 7: Diameter = 18 in
Circumference = 3.14 × 18
→ 3 × 18 = 54
0.14 × 18 = 2.52
Total = 54 + 2.52 =
56.52 in
✔ Check: 3.14 × 18 = 56.52 → correct.
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Problem 8: Diameter = 10 yd
Circumference = 3.14 × 10 =
31.4 yd
✔ Simple: move decimal — 3.14 × 10 = 31.4 → correct.
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Problem 9: Diameter = 4 yd
Circumference = 3.14 × 4
→ 3 × 4 = 12
0.14 × 4 = 0.56
Total = 12 + 0.56 =
12.56 yd
✔ Check: 3.14 × 4 = 12.56 → correct.
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Final Answer:
1. 113.04 yd
2. 37.68 ft
3. 43.96 in
4. 94.2 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 finding the area of a circle worksheet.
