Add angles, and find a missing angle
Finding a missing angle is one of your child's first chances to solve for an unknown, by writing something like 35 + ? = 90, and that habit is a quiet step toward algebra. In middle school, the same reasoning is how they find missing angles inside triangles, around a point, and where two lines cross, and it shows up later in building and design.
In this video, your child will learn to add angles and find missing angles.
The lesson stops at each question for your child's answer.
Three problems, each a little harder
Each problem is worked step by step. Your child will solve the last one before Bobby shows how.
Example 1
30° + 50° = ?
Example 2
35° + ? = 90°
Your child's turn
128° + ? = 180°
The three key steps
- 1The whole is the parts added
- 2Missing part: whole − part
- 3Square 90°, straight line 180°
Mistakes to listen for
- 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.
The lesson shows every step, so your child sees why it works. Read our parent's guide to adding angles together to find a missing one →
Is your child ready to practice what they've learned?
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Questions parents ask
Does my child need an account to watch?
No. You can watch this on any device at any time. If your child would like to practice adding angles together to find a missing one, and you'd like parent-friendly reports on your child's progress and growth, you can join Bobby's Math Club for unlimited free practice.
What happens when my child answers a question?
A right answer gets a cheer, and the lesson carries on. If your child isn't sure, they can tap "I don't know yet", and Bobby gives the answer and shows another example. Nothing is scored or stored.
Is this the same lesson that's on YouTube?
Yes. Here, the lesson stops at each question and waits for your child to answer. On YouTube, each question stays on screen for a few seconds, and then the lesson plays on.
Where can I learn more?
There's a short, kid-friendly lesson like this one for every Pre-K to 5th grade math skill, all in our video library. Our parent's guide to adding angles together to find a missing one has more on where kids get stuck and how you can help at home. In the club, your child practices at just the right level, about five minutes a day, and you get parent-friendly reports as they grow. Learn more about how it works →
Practice adding angles together to find a missing one
Questions at your child's level, about five minutes a day, on adding angles together to find a missing one and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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