Skill: Complete input-output tables

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An input-output table represents a consistent relationship in which each output is determined from its corresponding input by a simple rule, such as adding or subtracting a fixed whole number within 100. Completing the table requires applying the rule accurately, using the inverse operation when an input is missing, and recognizing that the same relationship holds in every row; symbolic formulas, variables, and more complex rules are not included.

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Detailed Explanation: Complete input-output tables

An input-output table follows the same rule in every row. First, use a row with both numbers to find the rule.

Input	Output
8	15
21	?
?	40

From the first row, $8$ becomes $15$ by adding $7$ :

8+7=15

So the rule is add 7.

Use the rule to find the missing output:

21+7=28

Now use the inverse operation to find the missing input. Ask, “What number plus $7$ equals $40$ ?” Subtract $7$ :

40-7=33

The completed table is:

Input	Output
8	15
21	28
33	40

Always use the same rule in every row. When the input is missing, use the inverse operation.

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Input/Output Tables (Add/Subtract) - Table with Gap to Missing Value

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