How to Find a Missing Angle
Angles that sit side by side add together.
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How to do it
- Find the whole angle.
- Subtract the part you know.
- Check that the parts add up.
Teaching tip
Write the whole angle first, then the subtraction. This sheet is aligned with Common Core 4.MD.C.5.
About this chart
Missing angles in a marked angle, on a straight line (180°) and in a square corner (90°).
What kids practice
An angle is two rays that share an endpoint, called the vertex. Angles are measured in degrees. A full turn is 360°, a right angle is 90° and a straight angle is 180°. Fourth graders sort angles as acute, right or obtuse, measure and draw angles with a protractor, and add or subtract angles to find a missing one.
Watch for
- Reading the wrong scale, like 130° for a 50° angle.
- Putting the edge of the protractor, not the center mark, on the vertex.
- Thinking longer rays make a bigger angle.
- Adding instead of subtracting to find a missing part.
It's free to print, as many copies as you need. See the full angles guide for 4th grade.
More sheets in this set
- See it all
1. How to Name AnglesThe parts of an angle, acute, right, obtuse and straight angles, and turns in degrees. 
2. Acute, Right or Obtuse?Angles in many directions to sort. More adds straight angles.- See it all
3. How to Use a ProtractorReading a 50° angle on the outer scale and a 130° angle on the inner scale. 
4. Read the ProtractorProtractors drawn on angles to read. Fewer uses tens, Standard uses fives on both scales, and More uses any whole degree.
5. Measure AnglesAngles to measure with a real protractor. Fewer uses tens, and Standard and More use fives in different directions.
6. Draw AnglesA ray and a measure to draw each angle with a protractor.
8. Find the Missing AngleAngles split into parts to find the missing one. Fewer uses marked angles and straight lines, Standard adds square corners, and More has three parts.