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Solve one-step subtraction equations

This understanding involves finding an unknown whole number in one-step subtraction equations within 100, whether the unknown is the difference, the starting quantity (minuend), or the quantity removed (subtrahend). Learners interpret subtraction as a relationship between three quantities, use the inverse relationship with addition and representations such as number lines or bar models to reason and verify solutions, rather than treating subtraction only as taking away; negative numbers, decimals, and multi-step or generalized equations are outside this scope.

Detailed Explanation: Solve one-step subtraction equations

Subtraction compares three quantities:

  • the starting amount,
  • the amount taken away,
  • the amount left.

You can use addition to find a missing part because addition and subtraction are opposites.

Example:

14−□=814-\square=8

Step 1: Think about what is missing.
We started with 1414 and have 88 left. The missing number is the amount taken away.

Step 2: Use addition to find the missing part.
Ask: “What number can I add to 88 to make 1414?”

8+□=148+\square=14

Count on from 88 to 1414:

9, 10, 11, 12, 13, 149,\ 10,\ 11,\ 12,\ 13,\ 14

That is 66 numbers, so □=6\square=6.

Step 3: Check your answer.

14−6=814-6=8

The equation is true, so the missing number is:

6\boxed{6}

Learn by doing: Solve one-step subtraction equations

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