Subtraction Within 20
Subtraction within 20 means taking away when the starting number is between 10 and 20. The answer can be anything from 0 to 20.
We can use counting back, using 10, or thinking of addition to find the answer.
What is Subtraction Within 20 - Class 1 Maths (Subtraction (Grade 1))?
Subtraction within 20 includes problems like 15 − 7, 18 − 9, 13 − 5. To solve bigger subtractions, we can subtract through 10:
- First subtract to reach 10.
- Then subtract what is left.
Example: 15 − 7 → 15 − 5 = 10, then 10 − 2 = 8.
Solved Examples
Example 1: 13 − 5
Question: What is 13 − 5?
Think:
- 13 − 3 = 10 (subtract to reach 10)
- Still need to subtract 2 more (since 5 = 3 + 2)
- 10 − 2 = 8
Answer: 13 − 5 = 8.
Example 2: 16 − 9
Question: What is 16 − 9?
Think:
- 16 − 6 = 10
- Still need to subtract 3 more (since 9 = 6 + 3)
- 10 − 3 = 7
Answer: 16 − 9 = 7.
Example 3: 15 − 5
Question: What is 15 − 5?
Think:
- 15 has 1 ten and 5 ones
- Take away the 5 ones
- Only 10 is left
Answer: 15 − 5 = 10.
Example 4: 18 − 8
Question: What is 18 − 8?
Think:
- 18 = 10 + 8
- Take away 8: only 10 remains
Answer: 18 − 8 = 10.
Example 5: Ria's Stickers
Question: Ria has 17 stickers. She gives 8 to Priya. How many does Ria have left?
Think:
- 17 − 7 = 10
- Still need to take 1 more: 10 − 1 = 9
Answer: Ria has 9 stickers left.
Example 6: 20 − 5
Question: What is 20 − 5?
Think:
- 20 − 5: Count back 5 from 20: 19, 18, 17, 16, 15
Answer: 20 − 5 = 15.
Example 7: Think Addition
Question: 14 − 6 = ?
Think:
- Think: 6 + ? = 14
- 6 + 8 = 14
- So 14 − 6 = 8
Answer: 14 − 6 = 8.
Key Points to Remember
- For subtraction within 20, use the subtract through 10 strategy.
- First subtract to reach 10, then subtract the rest.
- You can also think addition: if 14 − 6 = ?, think 6 + ? = 14.
- Subtracting the ones digit from a teen number leaves 10: 17 − 7 = 10.
- Check your answer with addition: if 15 − 8 = 7, then 7 + 8 = 15 ✓.
Practice Problems
- What is 14 − 7?
- What is 19 − 9?
- Aman has 16 crayons. He loses 8. How many are left?
- Find: 12 − 5.
- Think addition to solve: 11 − 4 = ?
- What is 20 − 10?
Frequently Asked Questions
Q1. What is subtraction within 20?
It means subtracting numbers where the starting number is 20 or less. Examples: 15−7=8, 18−9=9.
Q2. What is the 'subtract through 10' strategy?
First subtract enough to reach 10, then subtract the rest. For 14−6: take 4 away to get 10, then take 2 more to get 8.
Q3. What does 'think addition' mean?
Instead of subtracting, think: what number added to the smaller number gives the bigger number? For 13−5, think 5+?=13, so ?=8.
Q4. What is 20 − 10?
20 − 10 = 10. Take away 1 ten from 2 tens, and 1 ten is left.
Q5. How do I check my subtraction?
Add the answer to the number you subtracted. If it equals the starting number, you are correct. Example: 16−9=7, check: 7+9=16 ✓.
Q6. Is subtraction within 20 harder than within 10?
It can be, because the numbers are bigger. But using strategies like 'subtract through 10' and 'think addition' makes it manageable.
