An addition equation represents an equality between two quantities, with an unknown whole-number addend or sum that can occur in either addend position, such as , , or . The learner reasons that subtraction finds an unknown addend, using the inverse relationship between addition and subtraction and checking that both sides remain equal; representations such as number lines and bar models clarify this relationship. The scope excludes negative numbers, fractions, decimals, and multi-step or highly generalized equations.
An addition equation shows that two amounts are equal. To find an unknown addend, use subtraction because subtraction undoes addition.
Example:
Here, is the unknown number. We know the whole is , and one part is . Subtract the known part from the whole:
Now calculate:
So,
Check your answer by replacing with :
The equation is true, so the answer is correct. The unknown number is .
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