Finding the Missing Number Worksheet

Finding the missing number is an important first grade math skill that builds number sense and a strong understanding of how addition and subtraction work together. When children learn to find an unknown number in an equation, they begin to see that the equal sign means “the same as” and that they can work backward from an answer. This Finding the Missing Number Worksheet gives first graders focused practice determining the unknown number in addition and subtraction sentences within 20, helping them think flexibly about part-part-whole relationships.

This missing number addition and subtraction worksheet presents eight friendly equations, each with a number missing in a different spot — sometimes an addend, sometimes the sum, and sometimes part of a subtraction sentence. Students write the number that makes each equation true, then check their work against the included answer key. Use it as morning work, a quick review, a math center activity, or homework, and let students solve independently or explain their thinking out loud with a partner.

What’s Included

• 1 print-ready PDF worksheet
• Answer key
• 8 missing number addition and subtraction problems within 20

There are three big reasons this resource helps children grow. First, finding the missing number strengthens fact fluency, because students often use a fact they already know to figure out the unknown one. Second, mixing addition and subtraction on the same page helps children notice how the two operations are connected. Third, this Finding the Missing Number Worksheet keeps every problem within 20 and uses clear, uncluttered equations, so first graders can focus on their reasoning instead of getting lost in a busy page.

Teachers and parents can extend the learning in playful ways. Try building the same equations with counters, blocks, or a number line and letting children physically add or take away objects to discover the missing amount. Turn it into a game by covering one number in a fact your child already knows and asking, “What’s hiding?” You can also invite students to write their own missing number puzzles for a friend or family member to solve, which deepens their understanding while keeping the practice fun.

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