Subtraction within 20
"Subtract by taking away, crossing out objects, and counting backward up to 20."
A Today you'll learn
- Understand subtraction as taking away or finding how many are left
- Subtract numbers within 20 by crossing out pictures and counting backward
- Solve simple real-life subtraction stories
B Let's understand
Subtraction means taking some items away from a group and seeing how many are left. We use the minus sign (-) for subtraction. For example, imagine you have 8 tasty strawberries. If you eat 3 of them, you have 8 - 3 = 5 strawberries left on your plate! When you subtract 0 from any number, nothing is taken away, so the number stays exactly the same (6 - 0 = 6). If you take away all the items, you have 0 left (5 - 5 = 0).
C See it step by step
- Start with 10 apples.
- Take away 3: 10 - 3.
- Count backwards from 10 three times: 9, 8, 7.
- There are 7 apples left in the bowl.
- Start at 15 on the number line.
- Jump backward 4 steps: 14, 13, 12, 11.
- 15 - 4 = 11.
D Your turn
E Ready to practise?
Key idea 1
Subtraction means taking away or finding the difference.
The symbol - means "minus" or "subtract"
The symbol - means "minus" or "subtract".
When you take away 0
When you take away 0, the number does not change (e.g., 9 - 0 = 9).
Key idea 4
When you take away the same number from itself, the answer is 0 (7 - 7 = 0).
Key idea 5
Counting backward is a quick way to subtract.