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Skill: Solve missing-part word problems

Explanation and Free Practice Resources

Missing-part word problems involve determining an unknown quantity in a joining, separating, or part–part–whole situation, with quantities generally within 20. The learner interprets the relationship between the known parts and whole, represents it with a bar model, number line, or equation such as □ + 7 = 12 or 12 − 7 = □, and understands addition and subtraction as related operations rather than choosing an operation from keywords; multi-step problems, larger numbers, and generalized algebraic treatment are not included.

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Detailed Explanation: Solve missing-part word problems

A missing-part problem gives you the whole and one part. You find the part that is missing.

Example:
There are 12 apples. Seven apples are red, and the rest are green. How many apples are green?

  1. Find the whole: There are 12 apples altogether.
  2. Find the known part: 7 apples are red.
  3. The green apples are the missing part.

You can show the problem with a bar model:

7 red apples+? green apples=12 apples\boxed{7\text{ red apples}}+\boxed{?\text{ green apples}}=\boxed{12\text{ apples}}

Write an equation:

7+□=127+\square=12

Think: “What number goes with 7 to make 12?” Count on from 7:

8, 9, 10, 11, 128,\ 9,\ 10,\ 11,\ 12

That is 5 numbers, so:

7+5=127+5=12

The missing part is 5 green apples.

Learn by doing: Solve missing-part word problems

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    Addition - Missing Value, Within 20

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