Maryland Math 4.GR.B.7
The Standard
Explain that when an angle is decomposed into non-overlapping parts, the angle measure of the whole is the sum of the angle measures of the parts. Solve addition and subtraction problems to find unknown angles on a diagram in context (e.g., by using an equation with a symbol for the unknown angle measure).
Maryland College and Career Ready Standards for Mathematics (2025) · UNDERSTAND CONCEPTS OF ANGLE AND MEASURE ANGLES.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students show that two angle parts that do not overlap add up to the whole angle. They use addition or subtraction to find a missing angle in a diagram.
What Mastery Looks Like
- Given a split angle, a student identifies which parts make up the whole. They write an equation such as 38° + x° = 90°, solve for x, and check that the parts add to 90°.
Common Misconceptions
- Some students add a known part to the whole instead of subtracting it to find the missing part. Others count overlapping angles twice or think a longer ray makes a larger angle.
How to Assess It
- Give students a diagram of a 120° angle split into 47° and x°. Ask them to write an equation, find x, and explain why they used subtraction.
Lesson moves
Ways to Teach It
Give pairs cardboard angle wedges and protractors; have them draw a dividing ray, measure both parts, and check against the whole.
Show a 90° corner split into 35° and an unknown angle, then ask students to explain why they would subtract 35°.
Give pairs cards with split-angle diagrams and number cards; have them match each diagram to its missing angle measure.
Sketch a rectangular garden corner with a path 32° from one edge, then find the angle between the path and the other edge.
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