Whats the perimeter? | 3rd grade Math Worksheet | GreatSchools - Free Printable

Let's solve the perimeter problems in the image step by step.

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🔷 Understanding Perimeter

The perimeter of a shape is the total length around its edges. For rectangles, the formula is:

$$
\text{Perimeter} = 2 \times (\text{length} + \text{width})
$$

For squares, since all sides are equal:
$$
\text{Perimeter} = 4 \times \text{side}
$$

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✔ Problem 1: Top Rectangle (Example)

- Length = 5 cm
- Width = 4 cm

$$
\text{Perimeter} = 2 \times (5 + 4) = 2 \times 9 = 18 \, \text{cm}
$$

✔ The answer shown in the box is 20 cm, but that’s incorrect based on the given dimensions.

Wait — let’s double-check the diagram.

Looking closely at the top rectangle:
- It shows 5 cm on the top and 4 cm on the side.
- But the arrow box says 20 cm — which would be correct only if it were a square of 5 cm, or if both sides were 5 and 5.

But here:
- If it's 5 cm × 4 cm, then:
$$
P = 2(5 + 4) = 18 \, \text{cm}
$$

But the box says 20 cm — so maybe the dimensions are misread?

Wait — perhaps the rectangle has:
- One side labeled 5 cm, and the other side 5 cm? That would make it a square.

But no — the width is clearly labeled as 4 cm.

Wait — perhaps there’s an error in the image or in our interpretation.

But looking again — the top rectangle has:
- Top side: 5 cm
- Left side: 4 cm

So it’s a rectangle with length 5 cm, width 4 cm

Then:
$$
P = 2(5 + 4) = 2 \times 9 = 18 \, \text{cm}
$$

But the answer box says 20 cm — this suggests either:
- A mistake in the image,
- Or the rectangle is actually 5 cm × 5 cm (square), but the side is labeled 4 cm?

Wait — maybe the arrow box is showing the correct answer, so perhaps the rectangle is 5 cm × 5 cm?

But the left side is labeled 4 cm, not 5 cm.

This is inconsistent.

Alternatively, maybe the rectangle is 5 cm × 5 cm, and the 4 cm label is a typo?

Or perhaps I'm misreading.

Let’s look carefully.

Wait — the top rectangle:
- Top: 5 cm
- Right side: 4 cm
- Bottom: 5 cm
- Left side: 4 cm

So yes: 5 cm × 4 cm → perimeter = 2(5+4) = 18 cm

But the answer box says 20 cm — which is incorrect.

Unless... the rectangle is 5 cm × 5 cm — then P = 20 cm.

But the side is labeled 4 cm.

Possibility: Maybe the 4 cm is not the width? But it's drawn vertically.

Wait — could it be that the rectangle is 5 cm × 5 cm, and the 4 cm is a typo?

But no — the image shows:
```
5 cm
+-------+
| |
| 4 cm|
| |
+-------+
```

So it’s definitely 5 cm long, 4 cm wide.

So correct perimeter = 18 cm

But the answer box says 20 cm — this appears to be an error.

But wait — maybe the rectangle is not 5 cm × 4 cm?

Wait — perhaps the 5 cm is the diagonal? No — it’s labeled along the top edge.

No — it's a standard rectangle.

So likely, the answer box is wrong.

But since this is a worksheet, and the instruction says "Write the perimeter...", we should calculate correctly.

So for now, we'll assume the given labels are correct, and ignore the answer box unless it matches.

Let’s proceed to solve each shape one by one.

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## 🔢 Solving Each Shape

We’ll go from top to bottom, left to right.

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🟦 Shape 1: Top Rectangle

- Length = 5 cm
- Width = 4 cm
- Perimeter = 2 × (5 + 4) = 2 × 9 = 18 cm

✔ Answer: 18 cm

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🟨 Shape 2: First Row, Left

- Dimensions: 3 cm (top), 6 cm (left)
- So: length = 6 cm, width = 3 cm
- Perimeter = 2 × (6 + 3) = 2 × 9 = 18 cm

✔ Answer: 18 cm

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🟩 Shape 3: First Row, Right

- Dimensions: 4 cm (top), 8 cm (left)
- So: length = 8 cm, width = 4 cm
- Perimeter = 2 × (8 + 4) = 2 × 12 = 24 cm

✔ Answer: 24 cm

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🟪 Shape 4: Second Row, Left

- Dimensions: 4 cm (top), 6 cm (left)
- So: length = 6 cm, width = 4 cm
- Perimeter = 2 × (6 + 4) = 2 × 10 = 20 cm

✔ Answer: 20 cm

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🟫 Shape 5: Second Row, Middle

- Dimensions: 7 cm (top), 2 cm (left)
- So: length = 7 cm, width = 2 cm
- Perimeter = 2 × (7 + 2) = 2 × 9 = 18 cm

✔ Answer: 18 cm

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🟥 Shape 6: Second Row, Right

- Dimensions: 8 cm (top), 4 cm (left)
- So: length = 8 cm, width = 4 cm
- Perimeter = 2 × (8 + 4) = 2 × 12 = 24 cm

✔ Answer: 24 cm

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🟧 Shape 7: Third Row, Left

- Dimensions: 9 cm (top), 7 cm (left)
- So: length = 9 cm, width = 7 cm
- Perimeter = 2 × (9 + 7) = 2 × 16 = 32 cm

✔ Answer: 32 cm

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🟨 Shape 8: Third Row, Middle

- Dimensions: 12 cm (top), 5 cm (left)
- So: length = 12 cm, width = 5 cm
- Perimeter = 2 × (12 + 5) = 2 × 17 = 34 cm

✔ Answer: 34 cm

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🟬 Shape 9: Third Row, Right

- Dimensions: 10 cm (top), 5 cm (left)
- So: length = 10 cm, width = 5 cm
- Perimeter = 2 × (10 + 5) = 2 × 15 = 30 cm

✔ Answer: 30 cm

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✔ Final Answers (in order):

| Shape | Dimensions | Perimeter |
|-------|----------------|-----------|
| 1 | 5 cm × 4 cm | 18 cm |
| 2 | 6 cm × 3 cm | 18 cm |
| 3 | 8 cm × 4 cm | 24 cm |
| 4 | 6 cm × 4 cm | 20 cm |
| 5 | 7 cm × 2 cm | 18 cm |
| 6 | 8 cm × 4 cm | 24 cm |
| 7 | 9 cm × 7 cm | 32 cm |
| 8 | 12 cm × 5 cm | 34 cm |
| 9 | 10 cm × 5 cm | 30 cm |

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⚠️ Note on Top Example:

The top example shows a rectangle with 5 cm × 4 cm, but the answer box says 20 cm, which is incorrect.

Correct perimeter = 18 cm

So likely, either the label is wrong or the answer is wrong.

But based on the labels, 18 cm is correct.

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✔ Summary:

Students should write the following perimeters in the arrow boxes:

1. 18 cm
2. 18 cm
3. 24 cm
4. 20 cm
5. 18 cm
6. 24 cm
7. 32 cm
8. 34 cm
9. 30 cm

And correct the top example from 20 cm to 18 cm.

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If you're completing the worksheet, fill in the arrow boxes with these values.

Let me know if you'd like a printable version or a visual guide!