4th grade · Math · Unit 8 of 15
Polygons & Perimeter
Sides, symmetry and perimeter
What your child practices
Telling regular polygons (all sides and angles equal) from irregular ones, finding lines of symmetry, and measuring perimeter around regular and irregular shapes.
Maine Learning Results learning standard: 4.G.A.2; 4.G.A.3; 4.MD.A.3 · classifying shapes, lines of symmetry, and perimeter
How we explain it
Children can open this short lesson before they practice.
- Perimeter is the distance around a shape. Add all the sides.
- A regular polygon has all sides and angles equal.
- A line of symmetry splits a shape into matching halves.
Example: A rectangle is 17 m long and 11 m wide. What is its perimeter? Two lengths and two widths. 17 + 11 + 17 + 11 = 56. Answer: 56 m
Polygons & Perimeter in Maine
In the Maine Learning Results, this is unit 8 of 15 in 4th grade Math, after Equations and before Fractions.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Source: Maine Department of Education
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A rectangle is 20 m long and 16 m wide. What is its perimeter?
answer boxm
72 m
Hint: A rectangle has two long sides and two short sides. Add all four: 20 + 16 + 20 + 16. Or add 20 + 16 and double it.
Question 2
Which letter has NO line of symmetry?
- M
- W
- Z
Z
Hint: Imagine folding each letter. M and W can fold so the halves match, but Z can't fold that way.
Question 3
Which polygon is regular?
- rectangle
- trapezoid
- square
square
Hint: A regular polygon has all sides equal and all angles equal. All 4 sides are the same length and all 4 angles are equal.
Question 4
How many lines of symmetry does this shape have?
- 3
- 4
- 2
- 1
2
Hint: A line of symmetry is a fold line where both halves match exactly. Fold it top to bottom or side to side and the halves match. A diagonal fold doesn't match. That's 2.
Question 5
Each side of this square is 6 cm long. What is its perimeter?
answer boxcm
24 cm
Hint: Perimeter is the distance all the way around. A square has 4 equal sides, so multiply 4 × 6.
Question 6
Each square is 1 cm on a side. What is the perimeter of this rectangle?
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22 cm
Hint: Count the squares along the top (8) and down one side (3). Opposite sides match, so add 8 + 3 + 8 + 3.