Finding a missing addend means determining the unknown part in an addition equation, such as , by interpreting the total as the sum of two parts and using subtraction as the inverse of addition: . The reasoning applies to whole numbers within 1,000, including equations represented with place-value models, number lines, or bar models, and establishes fact-family relationships that support later work with multi-digit computation and algebraic equations; fractions, decimals, and more general unknown-value equations are not included.
When an addition equation has a missing addend, subtract the known addend from the total.
In the equation
Use subtraction to find the missing part:
Subtract by place value:
So,
The missing addend is .
Check by adding:
Therefore,
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