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.
Arizona Academic Standards 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 Arizona
In the Arizona Academic Standards, 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: Arizona 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
What kind of polygon is this?
- regular hexagon
- regular octagon
- irregular octagon
- irregular hexagon
regular hexagon
Hint: Count the sides: 6, so it is a hexagon. A regular polygon has all sides equal AND all angles equal. All 6 sides are the same length and all 6 angles are equal.
Question 2
A rectangle is 16 m long and 10 m wide. What is its perimeter?
answer boxm
52 m
Hint: A rectangle has two long sides and two short sides. Add all four: 16 + 10 + 16 + 10. Or add 16 + 10 and double it.
Question 3
How many lines of symmetry does this shape have?
- 5
- 3
- 8
- 4
4
Hint: A line of symmetry is a fold line where both halves match exactly. Fold a square top to bottom, side to side, or along either diagonal: all 4 folds match.
Question 4
Which letter has a line of symmetry?
- L
- V
- N
V
Hint: Imagine folding the letter. V can fold down the middle so both halves match exactly.
Question 5
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 (5) and down one side (6). Opposite sides match, so add 5 + 6 + 5 + 6.
Question 6
An irregular pentagon has these side lengths. What is its perimeter?
Side Length (cm) A 5 B 11 C 9 D 3 E 7 answer boxcm
35 cm
Hint: Perimeter is the distance all the way around, so add every side: 5 + 11 + 9 + 3 + 7. Tip: add pairs that are easy first.