Subtraction input/output tables – up to 18
key notes :
1. Understanding Input/Output Tables:
- Input/Output tables are a way to show how numbers change through an operation, like subtraction.
- The input is the number you start with, and the output is the result after subtracting a given number.
2. Subtraction Operation:
- Subtraction is taking away a number (called the subtrahend) from another number (called the minuend).
- For example, if the rule is “subtract 4,” and the input is 10, then 10 – 4 = 6 (output).
- Students need to understand basic subtraction facts up to 18, such as 18 – 2 = 16 or 15 – 7 = 8.
3. Recognizing the Rule:
- Each table follows a rule (like subtracting a fixed number from each input).
- The rule might be constant (e.g., subtracting 3 from all inputs) or may vary.
4. Filling in the Tables:
- Students are expected to complete tables where they are given either the input or the output.
- Example:
- Input: 10, 12, 15, 17
- Subtract 3 (Rule): 10 – 3 = 7, 12 – 3 = 9, etc.
- Output: 7, 9, 12, 14.
Learn with an example
Complete the table.
Rule: subtract 2
| In | Out |
| 2 | |
| 5 | |
| 6 | |
| 8 | 6 |
solution:
Start with the numbers in the “In” column. Subtract 2 from each number.
| 2 | − | 2 | = | 0 |
| 5 | − | 2 | = | 3 |
| 6 | − | 2 | = | 4 |
| 8 | − | 2 | = | 6 |
Write the answers in the table:
| In | Out |
| 2 | 0 |
| 5 | 3 |
| 6 | 4 |
| 8 | 6 |
Complete the table.
Rule: subtract 5
| In | Out |
| 5 | |
| 7 | |
| 8 | 3 |
| 9 |
solution:
Start with the numbers in the “In” column. Subtract 5 from each number.
| 5 | − | 5 | = | 0 |
| 7 | − | 5 | = | 2 |
| 8 | − | 5 | = | 3 |
| 9 | − | 5 | = | 4 |
Write the answers in the table:
| In | Out |
| 5 | 0 |
| 7 | 2 |
| 8 | 3 |
| 9 | 4 |
Complete the table.
Rule: subtract 1
| In | Out |
| 2 | |
| 7 | |
| 8 | 7 |
| 9 |
Start with the numbers in the “In” column. Subtract 1 from each number.
2 − 1 = 1
7 − 1 = 6
8 − 1 = 7
9 − 1 = 8
Write the answers in the table:
| In | Out |
| 2 | 1 |
| 7 | 6 |
| 8 | 7 |
| 9 | 8 |
Let’s practice!🖊️
