Skill: Solve one-step addition equations

Explanation and Free Practice Resources

This skill involves interpreting an equation as a statement that two quantities are equal and finding an unknown addend in whole-number addition equations within 100, whether the unknown appears before or after the known addend. Learners reason that subtraction can undo addition and use relationships among parts and the total, including related fact families, to determine and check the missing number; multi-step equations, negative numbers, and generalized symbolic algebra are outside this scope.

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Detailed Explanation: Solve one-step addition equations

An addition equation shows that both sides have the same value. To find a missing addend, subtract the known addend from the total.

Example:

\Box + 27 = 65

The total is $65$ , and one addend is $27$ .
Subtract the known addend from the total:

65 - 27 = 38

Write $38$ in the box:

38 + 27 = 65

Check by adding. Since $38 + 27 = 65$ , the missing number is $\boxed{38}$ .

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Addition - Missing Value, 2 Digit, 1 Number

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