Missing numbers, like 8 + ? = 11
In 1st grade, children learn to find the missing number in equations like 8 + ? = 11 or 5 = ? - 3 by thinking about how the three numbers relate.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 1st grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
What number makes this equation true: 6 + ? = 9
- 2
- 3
- 4
Why this matters
Solving a missing-number puzzle shows your child that they can reason their way to an answer, not only calculate one. It means seeing how three numbers fit together, which is exactly the thinking behind checking subtraction with addition. In 2nd grade the same puzzles use numbers up to 100, and in middle school the box becomes a letter: 8 + x = 11 is the same question your child is answering now.
Where kids can get stuck
- Adding the two numbers they see wherever the box is, so 8 + ? = 11 gets 19 instead of 3.
- Subtracting 3 from 5 to get 2 for ? - 3 = 5, when the missing number is really 8.
- Freezing when an equation starts with the single number, like 5 = ? - 3, because it looks unfamiliar.
How you can help
- Play a mystery number game: "I'm thinking of a number. If I add 4 to it, I get 9. What is my number?" Then let your child make up one for you.
- Use a cup to hide some coins. Say, "There are 11 coins altogether and 8 are outside the cup. How many are under it?" Lift the cup to check.
- Make number families with three objects or cards, such as 4, 6, and 10, and ask your child to say all the true addition and subtraction sentences they can.
The kid-friendly video below explains it in a few minutes, and Bobby's Math Club offers free practice that grows with your child.
Kid-friendly explanation
Questions parents ask
Why is my child learning to solve equations with a missing number?
These problems teach your child to think about how numbers relate instead of following one fixed step. Finding the missing part in 7 + ? = 10 builds understanding of both addition and subtraction at once. It also lays early groundwork for algebra, where unknown values are found in the same way.
What if my child always adds the numbers they see?
That is a very common habit. Ask your child to read the equation aloud as a question, such as "8 plus what makes 11?" Then use objects to act it out. Starting with 8 counters and adding more until there are 11 helps them see what the box really asks.
Are missing-number equations harder when the box is first?
Yes. Equations like ? + 4 = 9 or ? - 2 = 6 are usually harder because children do not know the starting amount. Turning them around can help: ? + 4 = 9 is the same as 4 + ? = 9. Practice with small numbers and real objects before moving to bigger numbers.
Make learning math fun
Bobby's Math Club turns 1st grade math practice into something fun to do together.
- Unlimited practice, completely free
- Questions matched to your child’s level, a few minutes a day
- Level-ups, badges, and a cheer for every win
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.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 1.OA.D.8: “Determine the unknown whole number in an addition or subtraction equation relating three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = ? - 3, 6 + 6 = ?.” Learn how Bobby's Math Club can help your students grow. (Common Core 1.OA.8)