Subtraction Within 20
Grade 1 · Math · Study Guide
Learn how to subtract numbers to find out how many are left.
Subtraction means taking away from a group to find out how many are left. We use a minus sign (-) to show subtraction. For example, 10 - 4 = 6 means if you start with 10 cookies and eat 4, you have 6 left.
One way to subtract is to count back. Start at the bigger number and count backwards. For 12 - 3, start at 12 and count back three: 11, 10, 9. Another way is to think about addition. If you know 5 + 6 = 11, then you also know 11 - 6 = 5. Addition and subtraction are like a team!
Subtracting zero from any number gives you that same number back. And when you subtract a number from itself — like 8 - 8 — the answer is always zero. You can also use a number line, hopping backward instead of forward.
| Addition Fact | Related Subtraction Fact |
|---|---|
| 6 + 7 = 13 | 13 - 7 = 6 |
| 8 + 5 = 13 | 13 - 5 = 8 |
| 9 + 6 = 15 | 15 - 6 = 9 |
| 7 + 8 = 15 | 15 - 8 = 7 |
Key terms
- subtraction
- Taking away a number from another to find the difference
- difference
- The answer you get when you subtract
- minus sign (-)
- The symbol that means subtract or take away
- count back
- A strategy where you start at the larger number and count down
- fact family
- A group of related addition and subtraction facts that use the same three numbers
Flashcards
- 13 - 5
- 8
- 16 - 7
- 9
- Difference
- The answer to a subtraction problem
- 12 - 4
- 8
- 18 - 9
- 9 (doubles subtraction fact)
- Fact Family
- Three numbers that go together in addition and subtraction facts, like 3, 7, and 10
Practice questions
What is 14 - 6?
- 7
- 9
- 8
- 6
Show answer
Answer: 8
14 - 6 = 8; count back 6 from 14 or think 6 + 8 = 14
7 - 7 = 0
Show answer
Answer: True
Any number minus itself equals zero
15 - 8 = ___
Show answer
Answer: 7
15 - 8 = 7; related addition fact is 8 + 7 = 15
Sam had 12 grapes. He ate 5. How many grapes are left?
- 6
- 8
- 7
- 9
Show answer
Answer: 7
12 - 5 = 7; start at 12 and count back 5
If 9 + 6 = 15, what does 15 - 9 equal?
- 5
- 6
- 7
- 4
Show answer
Answer: 6
15 - 9 = 6 because 9 + 6 = 15 (fact family relationship)
Fun facts
- Subtraction is the opposite of addition — they undo each other!
- Ancient Egyptians used subtraction over 4,000 years ago to keep track of grain in their storehouses.
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