An input-output rule describes a consistent relationship in which the same operation changes each input number into its corresponding output, often shown in a table, diagram, or number pattern. Learners determine and apply simple one-step rules, such as adding or subtracting a fixed amount—and, in familiar small-number contexts, forming equal groups—to find missing inputs or outputs and distinguish the direction of the relationship; general formulas, variables, and multi-step rules are beyond this scope.
An input-output rule tells what to do to each input to get its output. Always work from left to right:
Look for the same change in the number pairs.
Example:
| Input | Output |
|---|---|
Compare the first pair:
becomes . This is adding .
Check another pair to make sure:
and . The rule works each time.
Use the rule on the last input:
So, the missing output is , and the rule is add .
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