4th Grade · Measurement & Data
4.MD.C.7: Add angles together, and find a missing angle
4.MD.C.7 is a 4th grade Common Core math standard in Measurement & Data. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
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.
In plain words
Add angles together, and find a missing angle.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 3
A ray splits an angle into two parts. What does the whole angle measure?
- 15°
- 75°
- 45°
Where students can get stuck
- Adding the parts and then the whole angle too, giving 150 degrees for an angle made of 30 and 45 degrees.
- Subtracting from the wrong total, using 180 instead of 90 for a right angle, and answering 145 instead of 55.
- Measuring the diagram with a protractor instead of using the numbers given, and landing a few degrees off.
Effective teaching strategies
- Draw a 75° angle split by a ray into a 30° part and a 45° part, and ask why the whole is 75°, not 150°.
- Mark a 35° part inside a square corner and have students find the other part by subtracting from 90°, then check that 35 + 55 = 90.
- Give a diagram labeled with two part angles and have students find the whole by adding, then check with a protractor and discuss small measuring differences.
Units that teach this standard
Find where 4.MD.C.7 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Go Math!
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Reveal Math
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Adding angles together to find a missing one for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice measurement and data at home
In Bobby's Math Club, students practice at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free for every family.
See how it works for teachers
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.