Circumference, Area, Radius, And Diameter Circle Worksheets - Free Printable

Let’s go through each problem one by one. We’ll use π = 3.14 as instructed, and round all answers to two decimal places.

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Problem 1:

Given: Radius = 16.1 cm
→ Diameter = 2 × radius = 2 × 16.1 = 32.2 cm
→ Area = π × r² = 3.14 × (16.1)² = 3.14 × 259.21 = 813.92 cm² *(Wait — the image says 8.05? That can’t be right. Let me recalculate carefully.)*

Hold on — something is wrong with the red answers in the image. For example, in Problem 1, if radius is 16.1 cm, area should be:

r² = 16.1 × 16.1 = 259.21
Area = 3.14 × 259.21 = let’s compute:

3 × 259.21 = 777.63
0.14 × 259.21 ≈ 36.2894
Total ≈ 777.63 + 36.29 = 813.92

But the image shows “Area = 8.05” — that’s way too small. Similarly, circumference = 2πr = 2 × 3.14 × 16.1 = 6.28 × 16.1

6 × 16.1 = 96.6
0.28 × 16.1 ≈ 4.508
Total ≈ 101.108 → rounded to two decimals: 101.11

But image says 10.4248 — again, off by factor of ~10.

This suggests the red answers in the image are incorrect, or perhaps mislabeled. But since the user uploaded this as a worksheet with red answers already filled in, maybe they want us to verify or correct them?

Wait — looking at Problem 2: diameter given as 8.5 in → so radius = 4.25 in → that matches.

Area = πr² = 3.14 × (4.25)² = 3.14 × 18.0625 = let's calculate:

3 × 18.0625 = 54.1875
0.14 × 18.0625 ≈ 2.52875
Total ≈ 56.71625 → rounded to two decimals: 56.72

But image says Area = 2.125 — again, way off.

Circumference = πd = 3.14 × 8.5 = 26.69 — that one matches!

So for Problem 2, circumference is correct, but area is not.

Similarly, Problem 3: radius = 10.9 ft → diameter = 21.8 ft → correct.

Area = 3.14 × (10.9)² = 3.14 × 118.81 = ?

3 × 118.81 = 356.43
0.14 × 118.81 ≈ 16.6334
Total ≈ 373.06 → rounded: 373.06

Image says 5.45 — no.

Circumference = 2πr = 2 × 3.14 × 10.9 = 6.28 × 10.9

6 × 10.9 = 65.4
0.28 × 10.9 ≈ 3.052
Total ≈ 68.452 — which matches the image! So circumference is correct, area is not.

Ah! I see the pattern now. The red answers for area in the image are completely wrong — likely someone forgot to square the radius or used diameter instead of radius without adjusting.

But wait — look at Problem 4: diameter = 30.4 in → radius = 15.2 in → correct.

Area = 3.14 × (15.2)² = 3.14 × 231.04 = ?

3 × 231.04 = 693.12
0.14 × 231.04 ≈ 32.3456
Total ≈ 725.4656 → rounded: 725.47

Image says 7.6 — nope.

Circumference = πd = 3.14 × 30.4 = 95.456 — matches image.

Same thing: circumference correct, area wrong.

Problem 5: radius = 8.92 ft → diameter = 17.84 ft → correct.

Area = 3.14 × (8.92)² = 3.14 × 79.5664 ≈ ?

First, 8.92²:

8.92 × 8.92:

= (9 - 0.08)² = 81 - 2×9×0.08 + (0.08)² = 81 - 1.44 + 0.0064 = 79.5664 — yes.

Now 3.14 × 79.5664:

3 × 79.5664 = 238.6992
0.14 × 79.5664 ≈ 11.139296
Total ≈ 249.8385 → rounded: 249.84

Image says 4.46 — way off.

Circumference = 2πr = 2 × 3.14 × 8.92 = 6.28 × 8.92

6 × 8.92 = 53.52
0.28 × 8.92 ≈ 2.4976
Total ≈ 56.0176 — matches image.

Again, circumference correct, area wrong.

Problem 6: diameter = 18.5 m → radius = 9.25 m → correct.

Area = 3.14 × (9.25)² = 3.14 × 85.5625

Calculate 9.25²:

9.25 × 9.25 = (9 + 0.25)² = 81 + 2×9×0.25 + 0.0625 = 81 + 4.5 + 0.0625 = 85.5625 — yes.

3.14 × 85.5625:

3 × 85.5625 = 256.6875
0.14 × 85.5625 ≈ 11.97875
Total ≈ 268.66625 → rounded: 268.67

Image says 4.625 — no.

Circumference = πd = 3.14 × 18.5 = 58.09 — matches.

Problem 7: radius = 11.6 m → diameter = 23.2 m → correct.

Area = 3.14 × (11.6)² = 3.14 × 134.56

11.6² = 134.56 — yes.

3.14 × 134.56:

3 × 134.56 = 403.68
0.14 × 134.56 ≈ 18.8384
Total ≈ 422.5184 → rounded: 422.52

Image says 5.8 — no.

Circumference = 2πr = 2 × 3.14 × 11.6 = 6.28 × 11.6

6 × 11.6 = 69.6
0.28 × 11.6 ≈ 3.248
Total ≈ 72.848 — matches image.

Problem 8: diameter = 26.2 ft → radius = 13.1 ft → correct.

Area = 3.14 × (13.1)² = 3.14 × 171.61

13.1² = 171.61 — yes.

3.14 × 171.61:

3 × 171.61 = 514.83
0.14 × 171.61 ≈ 24.0254
Total ≈ 538.8554 → rounded: 538.86

Image says 6.55 — no.

Circumference = πd = 3.14 × 26.2 = 82.268 → rounded to two decimals: 82.27

But image says 41.134 — that’s half! Wait — 2πr would be same as πd, so it should be 82.27.

Unless... did they use radius instead of diameter? If they did πr = 3.14 × 13.1 = 41.134 — ah! So for circumference, they mistakenly used πr instead of 2πr or πd.

In Problem 8, circumference should be πd = 3.14 × 26.2 = 82.27, but image has 41.134 — which is πr.

Similarly, in Problem 9: radius = 3.66 cm → diameter = 7.32 cm → correct.

Area = 3.14 × (3.66)² = 3.14 × 13.3956 ≈ ?

3.66² = 13.3956 — yes.

3.14 × 13.3956:

3 × 13.3956 = 40.1868
0.14 × 13.3956 ≈ 1.875384
Total ≈ 42.062184 → rounded: 42.06

Image says 1.83 — no.

Circumference = 2πr = 2 × 3.14 × 3.66 = 6.28 × 3.66

6 × 3.66 = 21.96
0.28 × 3.66 ≈ 1.0248
Total ≈ 22.9848 — matches image.

So summary:

- All diameters are correctly calculated from radii (or vice versa).
- All circumferences are correctly calculated EXCEPT Problem 8, where they used πr instead of πd (so got half the correct value).
- All areas are wildly incorrect — seems like they computed πr instead of πr², or used diameter without squaring properly.

But since the user provided the worksheet with red answers, and asked to "solve the problem accurately", I think we are meant to provide the correct answers, ignoring the red ones which are mostly wrong.

Also, note: in Problem 8, circumference is listed as 41.134, but should be 82.27.

Let me double-check Problem 8 circumference:

Diameter = 26.2 ft → Circumference = π × d = 3.14 × 26.2

Compute: 3.14 × 26.2

Breakdown: 3 × 26.2 = 78.6; 0.14 × 26.2 = 3.668; total = 82.268 → rounded to two decimals: 82.27

Yes.

Now, for areas, let’s list correct values for all problems.

We’ll do each one carefully.

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## Correct Calculations:

Use π = 3.14, round final answers to two decimal places.

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Problem 1:

Radius = 16.1 cm
Diameter = 2 × 16.1 = 32.20 cm
Area = πr² = 3.14 × (16.1)² = 3.14 × 259.21 =
→ 3.14 × 259.21 = let's compute exactly:

259.21 × 3 = 777.63
259.21 × 0.14 = 36.2894
Sum = 813.9194 → 813.92 cm²
Circumference = 2πr = 2 × 3.14 × 16.1 = 6.28 × 16.1
6.28 × 16 = 100.48; 6.28 × 0.1 = 0.628; total = 101.108 → 101.11 cm

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Problem 2:

Diameter = 8.5 in → Radius = 4.25 in
Diameter = 8.50 in
Area = 3.14 × (4.25)² = 3.14 × 18.0625 =
18.0625 × 3 = 54.1875
18.0625 × 0.14 = 2.52875
Sum = 56.71625 → 56.72 in²
Circumference = πd = 3.14 × 8.5 = 26.69 → 26.69 in

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Problem 3:

Radius = 10.9 ft
Diameter = 2 × 10.9 = 21.80 ft
Area = 3.14 × (10.9)² = 3.14 × 118.81 =
118.81 × 3 = 356.43
118.81 × 0.14 = 16.6334
Sum = 373.0634 → 373.06 ft²
Circumference = 2πr = 2 × 3.14 × 10.9 = 6.28 × 10.9
6.28 × 10 = 62.8; 6.28 × 0.9 = 5.652; total = 68.452 → 68.45 ft

(Note: earlier I said 68.452 rounds to 68.45, not 68.452 — but instruction says round to two decimal places, so 68.45)

Wait — 68.452 rounded to two decimals is 68.45? No: third decimal is 2 < 5, so yes, 68.45.

But in the image it was written as 68.452 — probably kept more digits, but we must round to two.

Actually, let's confirm rounding rules: look at third decimal digit. If >=5, round up second decimal.

68.452 → third digit is 2 → so 68.45

But in some contexts, they might keep three, but instruction says "round to two decimal places".

So we'll do that.

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Problem 4:

Diameter = 30.4 in → Radius = 15.2 in
Diameter = 30.40 in
Area = 3.14 × (15.2)² = 3.14 × 231.04 =
231.04 × 3 = 693.12
231.04 × 0.14 = 32.3456
Sum = 725.4656 → 725.47 in²
Circumference = πd = 3.14 × 30.4 = 95.456 → 95.46 in (since third decimal is 6 > 5, round up 5 to 6)

95.456 → look at hundredths place is 5, thousandths is 6 → so round up 5 to 6 → 95.46

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Problem 5:

Radius = 8.92 ft
Diameter = 2 × 8.92 = 17.84 ft
Area = 3.14 × (8.92)² = 3.14 × 79.5664 =
79.5664 × 3 = 238.6992
79.5664 × 0.14 = 11.139296
Sum = 249.838496 → 249.84 ft²
Circumference = 2πr = 2 × 3.14 × 8.92 = 6.28 × 8.92
6.28 × 8 = 50.24; 6.28 × 0.92 = 5.7776; total = 56.0176 → 56.02 ft (third decimal 7 > 5, so round up 1 to 2? Wait: 56.0176 → hundredths is 1, thousandths is 7 → so round up 1 to 2 → 56.02)

56.0176: digits after decimal: 0 (tenths), 1 (hundredths), 7 (thousandths) → since 7>=5, round up hundredths from 1 to 2 → 56.02

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Problem 6:

Diameter = 18.5 m → Radius = 9.25 m
Diameter = 18.50 m
Area = 3.14 × (9.25)² = 3.14 × 85.5625 =
85.5625 × 3 = 256.6875
85.5625 × 0.14 = 11.97875
Sum = 268.66625 → 268.67 m² (third decimal 6 > 5, round up 6 to 7)
Circumference = πd = 3.14 × 18.5 = 58.09 → 58.09 m (exactly, since 3.14 × 18.5 = 58.09)

3.14 × 18.5:

3 × 18.5 = 55.5
0.14 × 18.5 = 2.59
Total = 58.09 — yes, exact.

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Problem 7:

Radius = 11.6 m
Diameter = 2 × 11.6 = 23.20 m
Area = 3.14 × (11.6)² = 3.14 × 134.56 =
134.56 × 3 = 403.68
134.56 × 0.14 = 18.8384
Sum = 422.5184 → 422.52 m² (third decimal 8 > 5, round up 1 to 2)
Circumference = 2πr = 2 × 3.14 × 11.6 = 6.28 × 11.6
6.28 × 11 = 69.08; 6.28 × 0.6 = 3.768; total = 72.848 → 72.85 m (third decimal 8 > 5, round up 4 to 5)

72.848 → hundredths is 4, thousandths is 8 → round up 4 to 5 → 72.85

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Problem 8:

Diameter = 26.2 ft → Radius = 13.1 ft
Diameter = 26.20 ft
Area = 3.14 × (13.1)² = 3.14 × 171.61 =
171.61 × 3 = 514.83
171.61 × 0.14 = 24.0254
Sum = 538.8554 → 538.86 ft² (third decimal 5, so round up 5 to 6? Wait: 538.8554 → hundredths is 5, thousandths is 5 → round up → 538.86)
Circumference = πd = 3.14 × 26.2 = 82.268 → 82.27 ft (third decimal 8 > 5, round up 6 to 7)

Earlier image had 41.134, which is wrong — that’s πr, not πd.

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Problem 9:

Radius = 3.66 cm
Diameter = 2 × 3.66 = 7.32 cm
Area = 3.14 × (3.66)² = 3.14 × 13.3956 =
13.3956 × 3 = 40.1868
13.3956 × 0.14 = 1.875384
Sum = 42.062184 → 42.06 cm² (third decimal 2 < 5, so leave as 42.06)
Circumference = 2πr = 2 × 3.14 × 3.66 = 6.28 × 3.66
6.28 × 3 = 18.84; 6.28 × 0.66 = 4.1448; total = 22.9848 → 22.98 cm (third decimal 4 < 5, so 22.98)

22.9848 → hundredths is 8, thousandths is 4 → since 4<5, keep 8 → 22.98

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Now, compiling all correct answers:

Note: In the original worksheet, units are given per problem, so we include them.

Also, for consistency, we write all with two decimal places, even if trailing zero.

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Final Answer:

1)
Radius = 16.10 cm
Diameter = 32.20 cm
Area = 813.92 cm²
Circumference = 101.11 cm

2)
Radius = 4.25 in
Diameter = 8.50 in
Area = 56.72 in²
Circumference = 26.69 in

3)
Radius = 10.90 ft
Diameter = 21.80 ft
Area = 373.06 ft²
Circumference = 68.45 ft

4)
Radius = 15.20 in
Diameter = 30.40 in
Area = 725.47 in²
Circumference = 95.46 in

5)
Radius = 8.92 ft
Diameter = 17.84 ft
Area = 249.84 ft²
Circumference = 56.02 ft

6)
Radius = 9.25 m
Diameter = 18.50 m
Area = 268.67 m²
Circumference = 58.09 m

7)
Radius = 11.60 m
Diameter = 23.20 m
Area = 422.52 m²
Circumference = 72.85 m

8)
Radius = 13.10 ft
Diameter = 26.20 ft
Area = 538.86 ft²
Circumference = 82.27 ft

9)
Radius = 3.66 cm
Diameter = 7.32 cm
Area = 42.06 cm²
Circumference = 22.98 cm