A box in an addition or subtraction equation represents an unknown whole number, and the equation expresses a relationship among quantities rather than a command to calculate from left to right. Missing values may occur in any position, as in 7 + □ = 12, □ − 4 = 9, or 15 − □ = 8; they are found through counting, known facts, or inverse relationships while preserving the meaning of the equal sign. The focus is on whole numbers within 20, not generalized algebraic equations or formal variable manipulation.
A box stands for a number we do not know yet. Find the number that makes both sides of the equation equal.
Example:
Start with . Count up until you reach :
You counted numbers, so the box is .
Check that both sides have the same value. The equation is true, so:
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