4.MD.7: Add and Subtract Angle Measures
Also written as 4.MD.C.7 and CCSS.MATH.CONTENT.4.MD.C.7 · Cluster: Geometric measurement: understand concepts of angle and measure angles.
The Official Wording
Recognize angle measure as additive. 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 real world and mathematical problems, e.g., by using an equation with a symbol for the unknown angle measure.
Common Core State Standards, Grade 4, Measurement & Data · Read it at the source · Checked October 14, 2026
What 4.MD.7 Means in Plain English
Fourth graders see that angles add like lengths: a 35° angle next to a 55° angle, sharing a ray, makes a 90° angle. Turn it around and a missing piece is subtraction: if a right angle is split and one part is 62°, the other is 28°.
Students write it as an equation with a symbol, like 62 + □ = 90, and solve it in real settings such as a ramp or a door swinging open. In 7th grade the same facts become supplementary and vertical angle equations (7.G.5).
4.MD.7 I Can Statements
- I can explain that the parts of an angle add to the whole.
- I can find a missing angle with addition or subtraction.
- I can write an equation with a symbol for an unknown angle.
4.MD.7 Worked Example
A street corner where three angles share one straight line, solved with one equation.
Two side streets leave a straight road from the same corner, splitting the straight angle on one side of the road into three angles. Two of them measure 48° and 65°. What is the third?
- A straight road makes a straight angle, a half turn. That is the whole.whole = 180°
- The three angles do not overlap and fill the straight angle exactly, so their measures add to 180°.48 + □ + 65 = 180
- Add the two known parts.48 + 65 = 113
- The unknown angle is what is left of the 180°.180 − 113 = 67, so □ = 67°
Check it: Put the parts back together: 48 + 67 + 65 = 180, a full straight angle. And 67° is a bit less than a right angle, which fits a street that leaves the road at a slant.
Common Mistakes with 4.MD.7
Using 90 as the whole every time
48 + □ + 65 = 90 for angles along a straight line
Try this: Name the whole first: a square corner is 90°, a straight line is 180°, and a full turn is 360°.
Adding when the unknown is a part
A 90° angle split into 34° and □, answered 124°
Try this: Ask whether the unknown is the whole or one part. A missing part is the whole minus the parts already known.
Adding angles that overlap
A 30° angle inside a 70° angle, added to make 100°
Try this: Shade each part in its own color. Only angles that sit side by side, sharing one ray and no inside space, add up.
Where 4.MD.7 Fits
Practice 4.MD.7
Quick Check
- A right angle is split into two angles. One is 27°. What is the other?
- Angles of 110° and 45° sit side by side, sharing a ray. What angle do they make together?
- Three angles meet at a point and fill a full turn. Two are 120° and 150°. What is the third?