Missing Addends Within 20 Worksheets for 1st Grade
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Skill: Finding the unknown addend with sums from 11 to 20
Teaching tips and what to try next
A next step for first graders who are steady with Missing Addends Within 10 and know their pairs that make ten. Counting up from the known part to the total on a number strip shows how many are missing. The same thinking appears with subtraction in Missing Numbers in Subtraction Within 20.
10 versions, each with its own answer key
Same skill and layout, a fresh set of problems in every version, so children can keep practicing without repeating a page. Problems are not repeated between versions unless a skill has only a small number of possible problems (for example, the addition facts within 10).
- Version 1: Sheet · Key · Both
- Version 2: Sheet · Key · Both
- Version 3: Sheet · Key · Both
- Version 4: Sheet · Key · Both
- Version 5: Sheet · Key · Both
- Version 6: Sheet · Key · Both
- Version 7: Sheet · Key · Both
- Version 8: Sheet · Key · Both
- Version 9: Sheet · Key · Both
- Version 10: Sheet · Key · Both
Download all 10 versions (one PDF)All 10 answer keys (PDF)
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About this worksheet
Missing addend problems ask children to think about addition in a new way. Instead of finding the total, they know the total and one part and must find the other part, as in 8 + ___ = 15. This first-grade worksheet gives twenty of these equations with sums from 11 to 20, which is the next step after missing addends within 10.
Every equation has a total between 11 and 20, and both addends are at least 2. On some lines the first addend is missing, and on others the second addend is missing, so children must read each equation carefully instead of following a pattern. Each of the ten versions has new equations, and each comes with its own answer key.
How to use it: teach your child to ask, "What plus this number makes that number?" For 8 + ___ = 15, a child might count up from 8 to 15 on their fingers, or use a known fact: 8 + 2 = 10, and 5 more makes 15, so the answer is 7. Linking the problem to subtraction also works: 15 – 8 = 7. Encourage your child to check each answer by putting it back into the equation and adding. A common mistake is writing the total minus nothing, or adding the two numbers that are shown, so remind your child that the number after the equal sign is the whole.
The answer key shows every missing addend. For easier practice, try our Missing Addends Within 10 worksheet. For subtraction with unknowns, try our Missing Numbers in Subtraction Within 20 worksheet.