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Identify missing information

A mathematical situation may provide some quantities and relationships while omitting a quantity needed to answer its question. Reasoning about addition and subtraction with small whole numbers, especially within 20, involves distinguishing known, unknown, and irrelevant information, representing the relationships with an equation, number line, or bar model, and recognizing when a solution is not yet possible; multistep, unknown-parameter, and generalized cases are beyond this scope.

Detailed Explanation: Identify missing information

To identify missing information:

  1. Find the numbers and facts the problem gives you.
  2. Find what the question asks.
  3. Ask: “Do I know enough to find the answer?”
  4. Write an equation with a box for the missing number.

Example

Mia has 88 apples. She gives some apples away. How many apples does she have left?

  • We know Mia starts with 88 apples.
  • We know she gives apples away.
  • We do not know how many apples she gives away.
  • The question asks how many apples are left.

We could show the situation with an equation:

8−?=?8-\boxed{?}=\boxed{?}

Both the number given away and the number left are unknown. So, we cannot find one exact answer yet.

For example:

  • If Mia gives away 22, she has 66 left.
  • If Mia gives away 55, she has 33 left.

The problem needs one more fact, such as “Mia gives away 22 apples.” Then we can solve:

8−2=68-2=6

Mia would have 66 apples left.

Learn by doing: Identify missing information

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    Addition - Missing Value, Within 20

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