Fifth graders move past memorizing shape names and start using the (n − 2) × 180 formula like a real tool. You compute interior angle sums for pentagons (540°), octagons (1080°), and hexagons, and work backward from a 108° angle to identify a regular pentagon.
Vocabulary items separate convex from concave polygons and name the decagon. The matching task pairs each polygon — triangle, quadrilateral, pentagon, hexagon — with its angle sum, so you see the +180° pattern jump out as sides increase. That pattern, not the individual numbers, is what makes polygon angle reasoning stick.
Style:
Classifying 2D Shapes
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The sum of interior angles in a pentagon is 540 degrees.
2. Each interior angle of a regular hexagon measures 120 degrees.
3. A polygon with ten sides is called a decagon.
4. The formula for the sum of interior angles of a polygon is (n − 2) × 180 degrees.
5. A regular polygon with all angles equal to 108° has 5 sides.
6. The sum of interior angles in an octagon is 1080 degrees.
7. A polygon is convex if all its interior angles are less than 180°.
8. Each interior angle of a regular triangle (equilateral) measures 60 degrees.
9. A polygon that has at least one angle greater than 180° is called concave.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each polygon to its interior angle sum.
Triangle (3 sides)
→ 180°
540°
Quadrilateral (4 sides)
→ 360°
360°
Pentagon (5 sides)
→ 540°
720°
Hexagon (6 sides)
→ 720°
180°
Classifying 2D Shapes
★ Part A: Fill in the Blank
Write the missing word or number on each line.
1) The sum of interior angles in a pentagon is 540 degrees.
2) Each interior angle of a regular hexagon measures 120 degrees.
3) A polygon with ten sides is called a decagon.
4) The formula for the sum of interior angles of a polygon is (n − 2) × 180 degrees.
5) A regular polygon with all angles equal to 108° has 5 sides.
6) The sum of interior angles in an octagon is 1080 degrees.
7) A polygon is convex if all its interior angles are less than 180°.
8) Each interior angle of a regular triangle (equilateral) measures 60 degrees.
9) A polygon that has at least one angle greater than 180° is called concave.
★ Part B: Matching
Match each item on the left to the correct answer on the right.
1) Match each polygon to its interior angle sum.
Triangle (3 sides)
→ 180°
540°
Quadrilateral (4 sides)
→ 360°
360°
Pentagon (5 sides)
→ 540°
720°
Hexagon (6 sides)
→ 720°
180°
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10 Questions
10-15 minutes
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