Subtraction Within 20
Learn to take away numbers using counting back, crossing out and number lines!
What Is Subtraction?
Subtraction means taking away. When we subtract, we start with a number and take some away. The answer is always smaller.
We use the minus sign (−) to show subtraction, and the equals sign (=) to show the answer.
5 − 2 = 3
Start with 5, take away 2, and you have 3 left.
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Start with 5 apples
🍎🍎 ❌
Take away 2
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3 apples left!
Counting Back
One way to subtract is to count back. Start at the bigger number and count backwards.
Example: 8 − 3 = ?
Start at 8 and count back 3 times:
So 8 − 3 = 5
💡 Tip
You can use your fingers to keep track! Hold up 3 fingers and put one down each time you count back.
Using a Number Line
A number line helps us see subtraction. We hop backwards (to the left) to subtract.
Example: 12 − 4 = ?
Start at 12, hop back 4 places. You land on 8!
12 − 4 = 8
Worked Examples
Example 1: 7 − 3
Start with 7 counters. Cross out 3.
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Answer: 7 − 3 = 4
Example 2: 15 − 6
Count back from 15: 14, 13, 12, 11, 10, 9
Answer: 15 − 6 = 9
Example 3: 20 − 10
If you have 20 stickers and give away 10, how many are left?
Answer: 20 − 10 = 10
Knowledge Check
Choose the correct answer for each question. Questions get harder as you go!
1. What is 5 − 2?
2. What is 9 − 1?
3. You have 6 biscuits and eat 2. How many are left?
4. What is 10 − 4?
5. There are 13 birds on a fence. 5 fly away. How many are left?
6. What is 14 − 7?
7. You have 11 crayons. You lose 3. How many do you have now?
8. What is 17 − 9?
9. There are 20 children in a class. 8 go outside. How many stay inside?
10. I think of a number. I subtract 6 and get 11. What was my number?
Key Concepts Summary
- ●Subtraction means taking away. The answer is always smaller.
- ●Count back from the bigger number to subtract.
- ●Use a number line and hop backwards to find the answer.
- ●You can cross out objects to help you see the subtraction.
- ●Addition and subtraction are opposites — you can check your answer by adding!