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.
Alaska content standards learning standard: 4.G.2; 4.G.3; 4.MD.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 Alaska
In the Alaska content 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: Alaska Department of Education and Early Development
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
Which letter has NO line of symmetry?
- T
- S
- A
S
Hint: Imagine folding each letter. A and T can fold so the halves match, but S can't fold that way.
Question 2
An irregular pentagon has these side lengths. What is its perimeter?
Side Length (cm) A 7 B 8 C 5 D 8 E 2 answer boxcm
30 cm
Hint: Perimeter is the distance all the way around, so add every side: 7 + 8 + 5 + 8 + 2. Tip: add pairs that are easy first.
Question 3
Each square is 1 cm on a side. What is the perimeter of this rectangle?
🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦answer boxcm
30 cm
Hint: Count the squares along the top (9) and down one side (6). Opposite sides match, so add 9 + 6 + 9 + 6.
Question 4
How many lines of symmetry does this shape have?
- 4
- 2
- 1
- 3
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
A rectangle is 9 m long and 7 m wide. What is its perimeter?
answer boxm
32 m
Hint: A rectangle has two long sides and two short sides. Add all four: 9 + 7 + 9 + 7. Or add 9 + 7 and double it.
Question 6
Which polygon is regular?
- rectangle
- trapezoid
- hexagon
hexagon
Hint: A regular polygon has all sides equal and all angles equal. All 6 sides are the same length and all 6 angles are equal.