4th grade · Math · Unit 12 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.
Texas Essential Knowledge and Skills (TEKS) teks student expectation: 4.5(C); 4.6(B); 4.6(D) · perimeter formulas, lines of symmetry, and classifying two-dimensional figures
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 Texas
In the Texas Essential Knowledge and Skills (TEKS), this is unit 12 of 17 in 4th grade Math, after Angles & Area and before Triangles, Quadrilaterals & Angles.
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: Texas Education Agency (TEA)
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 polygon is regular?
- square
- trapezoid
- parallelogram
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 2
An irregular pentagon has these side lengths. What is its perimeter?
Side Length (cm) A 11 B 8 C 8 D 4 E 12 answer boxcm
43 cm
Hint: Perimeter is the distance all the way around, so add every side: 11 + 8 + 8 + 4 + 12. Tip: add pairs that are easy first.
Question 3
Which letter has NO line of symmetry?
- T
- O
- F
F
Hint: Imagine folding each letter. T and O can fold so the halves match, but F can't fold that way.
Question 4
How many lines of symmetry does this shape have?
- 6
- 7
- 5
- 12
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 5
What kind of polygon is this?
- irregular quadrilateral
- regular quadrilateral
- irregular pentagon
- regular pentagon
regular pentagon
Hint: Count the sides: 5, so it is a pentagon. A regular polygon has all sides equal AND all angles equal. All 5 sides are the same length and all 5 angles are equal.
Question 6
A rectangle is 14 m long and 8 m wide. What is its perimeter?
answer boxm
44 m
Hint: A rectangle has two long sides and two short sides. Add all four: 14 + 8 + 14 + 8. Or add 14 + 8 and double it.