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.
Alabama Course of Study content standard: 4.23; 4.28; 4.29 · 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 Alabama
In the Alabama Course of Study, 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.
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
An irregular pentagon has these side lengths. What is its perimeter?
Side Length (cm) A 11 B 8 C 9 D 4 E 11 answer boxcm
43 cm
Hint: Perimeter is the distance all the way around, so add every side: 11 + 8 + 9 + 4 + 11. Tip: add pairs that are easy first.
Question 2
Which letter has a line of symmetry?
- J
- O
- S
O
Hint: Imagine folding the letter. O can fold down the middle so both halves match exactly.
Question 3
What kind of polygon is this?
- regular triangle
- regular quadrilateral
- irregular quadrilateral
- irregular triangle
irregular quadrilateral
Hint: Count the sides: 4, so it is a quadrilateral. A regular polygon has all sides equal AND all angles equal. Its angles are all equal, but the long sides are longer than the short sides.
Question 4
A rectangle is 11 m long and 8 m wide. What is its perimeter?
answer boxm
38 m
Hint: A rectangle has two long sides and two short sides. Add all four: 11 + 8 + 11 + 8. Or add 11 + 8 and double it.
Question 5
Each square is 1 cm on a side. What is the perimeter of this rectangle?
🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦answer boxcm
24 cm
Hint: Count the squares along the top (8) and down one side (4). Opposite sides match, so add 8 + 4 + 8 + 4.
Question 6
Which polygon is regular?
- rectangle
- octagon
- parallelogram
octagon
Hint: A regular polygon has all sides equal and all angles equal. All 8 sides are the same length and all 8 angles are equal.