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Balance subtraction equations

Balance in subtraction equations means understanding the equal sign as stating that two quantities have the same value and determining a missing number so both sides remain equal, including forms such as 18−7=□18-7=\Box, 18−□=1118-\Box=11, or □−7=11\Box-7=11. Reasoning may connect subtraction with the difference between quantities and inverse addition, using number lines or bar models to preserve equivalence; at this level, the focus is on whole numbers within 100, not negative numbers, decimals, or generalized algebraic manipulation.

Detailed Explanation: Balance subtraction equations

The equal sign means both sides have the same value. To find a missing number in a subtraction equation, think about the related addition fact.

Example:

18−□=1118-\Box=11
  1. Ask: “What number added to 1111 makes 1818?”
11+□=1811+\Box=18
  1. Count up from 1111 to 1818:
11→12→13→14→15→16→17→1811\to12\to13\to14\to15\to16\to17\to18

That is 77 steps, so □=7\Box=7.

  1. Check the subtraction:
18−7=1118-7=11

Both sides equal 1111, so the balanced equation is:

18−7=1118-7=11

Learn by doing: Balance subtraction equations

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    Subtraction - Balance Equation - Two Digit, Three Terms

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