To find the perimeter of a shape, you add up the lengths of all its sides. Let’s go through each problem one by one.
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Problem 1:
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Square (2 in on each side):
All 4 sides are 2 inches.
Perimeter = 2 + 2 + 2 + 2 =
8 in
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Trapezoid (sides: 3 in, 2 in, 3 in, 6 in):
Add them: 3 + 2 + 3 + 6 =
14 in
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Right triangle (sides: 3 in, 4 in, 5 in):
Add them: 3 + 4 + 5 =
12 in
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Problem 2:
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Pentagon (all sides 3 m):
5 sides × 3 m =
15 m
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Hexagon (all sides 2 cm):
6 sides × 2 cm =
12 cm
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Octagon (all sides 1 in):
8 sides × 1 in =
8 in
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Problem 3:
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Irregular quadrilateral (sides: 3 in, 5 in, 5 in, 4 in):
Add: 3 + 5 + 5 + 4 =
17 in
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Irregular pentagon (sides: 3 ft, 3 ft, 3 ft, 3 ft, 6 ft):
Add: 3 + 3 + 3 + 3 + 6 =
18 ft
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Triangle (sides: 9 cm, 8 cm, 6 cm):
Add: 9 + 8 + 6 =
23 cm
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Problem 4:
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Star (each point has two sides of 3 in — total 10 sides? Wait — let’s count carefully.)
Looking at the star: it has 10 outer edges, each labeled “3 in”.
So: 10 × 3 =
30 in
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Cross shape (blue): Each arm is made of squares. Let’s trace the outer edge.
The cross has 12 outer sides, each 2 m long.
How? Think of it as a plus sign with equal arms. Each arm adds 3 segments to the perimeter? Actually, better way:
Count the outer edges: top, right, bottom, left — each “arm” contributes 3 sides of 2m? No — actually, for this standard cross made of 5 squares (center + 4 arms), the perimeter is 12 sides of 2m each.
Yes: 12 × 2 =
24 m
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Red octagon (each side 5 dm):
8 sides × 5 dm =
40 dm
Wait — let me double-check the cross:
The blue cross: if each small square is 2m per side, and it's shaped like a plus (+) with 5 squares (one center, four extending out), then the outer boundary has:
- Top arm: 3 sides exposed (top, left, right) → but wait, no — actually, when squares are joined, internal sides don’t count.
Standard cross made of 5 unit squares: perimeter is 12 units. Since each side is 2m, then 12 × 2 = 24m. Correct.
Now the star: it’s a 5-pointed star. Typically, such a star drawn with straight lines has 10 outer edges (each point has two sides). And each is labeled “3 in”, so 10 × 3 = 30 in. That matches.
Final check for red octagon: 8 sides × 5 dm = 40 dm. Correct.
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Final Answer:
1.
- Square:
8 in
- Trapezoid:
14 in
- Triangle:
12 in
2.
- Pentagon:
15 m
- Hexagon:
12 cm
- Octagon:
8 in
3.
- Quadrilateral:
17 in
- Pentagon:
18 ft
- Triangle:
23 cm
4.
- Star:
30 in
- Cross:
24 m
- Octagon:
40 dm
Parent Tip: Review the logic above to help your child master the concept of third grade perimeter worksheet.
