4th grade · Math · Unit 8 of 17
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.
New York State Learning Standards learning standard: NY-4.G.2; NY-4.G.3; NY-4.MD.3 · naming triangles and quadrilaterals, 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 New York
In the New York State Learning Standards, this is unit 8 of 17 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
A rectangle is 10 m long and 8 m wide. What is its perimeter?
answer boxm
36 m
Hint: A rectangle has two long sides and two short sides. Add all four: 10 + 8 + 10 + 8. Or add 10 + 8 and double it.
Question 2
An irregular pentagon has these side lengths. What is its perimeter?
Side Length (cm) A 5 B 7 C 11 D 6 E 5 answer boxcm
34 cm
Hint: Perimeter is the distance all the way around, so add every side: 5 + 7 + 11 + 6 + 5. Tip: add pairs that are easy first.
Question 3
Which letter has a line of symmetry?
- W
- G
- S
W
Hint: Imagine folding the letter. W can fold down the middle so both halves match exactly.
Question 4
Each side of this square is 8 cm long. What is its perimeter?
answer boxcm
32 cm
Hint: Perimeter is the distance all the way around. A square has 4 equal sides, so multiply 4 × 8.
Question 5
How many lines of symmetry does this shape have?
- 7
- 6
- 12
- 5
6
Hint: A line of symmetry is a fold line where both halves match exactly. A regular polygon has as many lines of symmetry as sides. This regular hexagon has 6.
Question 6
Which polygon is regular?
- pentagon
- rectangle
- parallelogram
pentagon
Hint: A regular polygon has all sides equal and all angles equal. All 5 sides are the same length and all 5 angles are equal.