Let’s solve each problem step by step.
We are told:
> Circumference = 2πr
> Assume π = 3.14
But note: sometimes the diagram gives
diameter (a line across the circle through the center), not radius.
Remember:
- If you’re given
diameter (d), then radius r = d ÷ 2
- So circumference can also be written as: C = π × d
We’ll use whichever is easier based on what’s given.
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Problem 1: Diameter = 42 yd
→ Use C = π × d = 3.14 × 42
Calculate:
3.14 × 40 = 125.6
3.14 × 2 = 6.28
Total = 125.6 + 6.28 =
131.88 yd
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Problem 2: Diameter = 22 ft
→ C = π × d = 3.14 × 22
3.14 × 20 = 62.8
3.14 × 2 = 6.28
Total = 62.8 + 6.28 =
69.08 ft
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Problem 3: Radius = 17 in
→ C = 2 × π × r = 2 × 3.14 × 17
First, 2 × 3.14 = 6.28
Then 6.28 × 17
Break it down:
6.28 × 10 = 62.8
6.28 × 7 = 43.96
Total = 62.8 + 43.96 =
106.76 in
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Problem 4: Radius = 91 yd
→ C = 2 × 3.14 × 91
First, 2 × 3.14 = 6.28
Now 6.28 × 91
Break into: 6.28 × 90 + 6.28 × 1
6.28 × 90 = 6.28 × 9 × 10 = (56.52) × 10 = 565.2
6.28 × 1 = 6.28
Total = 565.2 + 6.28 =
571.48 yd
Wait — let me double-check that multiplication:
Actually, better to do 6.28 × 91 directly:
6.28 × 90 = 565.2
6.28 × 1 = 6.28
Sum: 565.2 + 6.28 = 571.48 → Correct.
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Problem 5: Radius = 40 m
→ C = 2 × 3.14 × 40 = 6.28 × 40
6.28 × 4 = 25.12 → so ×10 = 251.2? Wait no:
6.28 × 40 = 6.28 × 4 × 10 = 25.12 × 10 =
251.2 m
Yes.
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Problem 6: Radius = 44 cm
→ C = 2 × 3.14 × 44 = 6.28 × 44
Calculate 6.28 × 40 = 251.2
6.28 × 4 = 25.12
Total = 251.2 + 25.12 =
276.32 cm
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Problem 7: Radius = 32 yd
→ C = 2 × 3.14 × 32 = 6.28 × 32
6.28 × 30 = 188.4
6.28 × 2 = 12.56
Total = 188.4 + 12.56 =
200.96 yd
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Problem 8: Diameter = 12.5 ft
→ C = π × d = 3.14 × 12.5
3.14 × 12 = 37.68
3.14 × 0.5 = 1.57
Total = 37.68 + 1.57 =
39.25 ft
Alternatively: 3.14 × 12.5 = (3.14 × 100/8) but easier as above.
Check: 3.14 × 12.5
= 3.14 × (25/2) = (3.14 × 25)/2 = 78.5 / 2 = 39.25 → same.
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All calculations verified.
Final Answer:
1. 131.88 yd
2. 69.08 ft
3. 106.76 in
4. 571.48 yd
5. 251.2 m
6. 276.32 cm
7. 200.96 yd
8. 39.25 ft
Parent Tip: Review the logic above to help your child master the concept of perimeter and circumference worksheet.
