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Choose addition or subtraction

The learner interprets single-step situations with whole numbers within 20 to determine whether addition models joining, combining, or finding a total, or subtraction models separating, comparing, or finding an unknown part or difference. Equations, part–part–whole diagrams, and number lines show that subtraction can represent more than “taking away” and is related to addition, so operation choice depends on the quantities and their relationships rather than on isolated keywords. Multi-step problems, larger-number algorithms, and generalized symbolic reasoning are outside this scope.

Detailed Explanation: Choose addition or subtraction

Read the problem and ask: Are quantities being joined to find a total, or are we finding a missing part or the difference between two amounts?

  • Use addition when groups are put together or a total is found.
  • Use subtraction when finding how many are left, how many more, or an unknown part.

Example

Mia has 8 crayons. Leo has 5 crayons. How many more crayons does Mia have than Leo?

  1. The crayons are not being joined. We are comparing the two amounts.

  2. We need to find the difference between 8 and 5, so use subtraction.

  3. Write the equation:

8−5=38-5=3
  1. The answer is 3 crayons. Mia has 3 more crayons than Leo.

You can check with addition:

5+3=85+3=8

So, subtraction is the right operation because we are finding the difference between two amounts.

Learn by doing: Choose addition or subtraction

Click a topic below to practice the foundational skills you'll need, learn the steps, or master this skill

    Practice with unlimited practice problems

    Picture Numbers - Subtracting - Picture and Instruction to Equation (Within 20)

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