Mental Addition and Subtraction
Mental maths means solving problems in your head, without writing anything on paper. In Class 2, children practice mental addition and subtraction with simple strategies.
Mental maths helps you calculate faster — useful when shopping, playing games, or answering quickly in class.
What is Mental Addition and Subtraction - Class 2 Maths (Addition (Grade 2))?
Mental addition and subtraction is doing calculations in your mind using smart tricks.
Common strategies:
- Adding 10: Just increase the tens digit by 1. 35 + 10 = 45.
- Subtracting 10: Decrease the tens digit by 1. 72 − 10 = 62.
- Adding 9: Add 10, then subtract 1. 46 + 9 = 46 + 10 − 1 = 55.
- Subtracting 9: Subtract 10, then add 1. 53 − 9 = 53 − 10 + 1 = 44.
- Make a ten: Break one number to make 10. 28 + 5 = 28 + 2 + 3 = 30 + 3 = 33.
Solved Examples
Example 1: Example 1: Add 10 mentally
Question: What is 47 + 10?
Think:
- Adding 10 means the tens digit goes up by 1
- 4 tens becomes 5 tens, ones stay 7
Answer: 47 + 10 = 57.
Example 2: Example 2: Subtract 10 mentally
Question: What is 83 − 10?
Think:
- Subtracting 10: tens digit goes down by 1
- 8 tens becomes 7 tens, ones stay 3
Answer: 83 − 10 = 73.
Example 3: Example 3: Add 9 (use add 10, subtract 1)
Question: Find 36 + 9 in your head.
Think:
- 9 is close to 10
- 36 + 10 = 46
- 46 − 1 = 45
Answer: 36 + 9 = 45.
Example 4: Example 4: Subtract 9 (use subtract 10, add 1)
Question: Find 62 − 9 in your head.
Think:
- 62 − 10 = 52
- 52 + 1 = 53 (we subtracted 1 extra, so add it back)
Answer: 62 − 9 = 53.
Example 5: Example 5: Make a ten
Question: Find 27 + 6 mentally.
Think:
- 27 needs 3 more to reach 30
- Break 6 into 3 + 3
- 27 + 3 = 30, then 30 + 3 = 33
Answer: 27 + 6 = 33.
Example 6: Example 6: Ria buys a pencil
Question: A pencil costs ₹9. Ria has ₹50. How much is left after buying the pencil?
Think:
- 50 − 9: Subtract 10 first → 40. Add 1 back → 41
Answer: Ria has ₹41 left.
Example 7: Example 7: Add 20 mentally
Question: What is 35 + 20?
Think:
- Adding 20 = adding 2 tens
- 3 tens + 2 tens = 5 tens. Ones stay 5.
Answer: 35 + 20 = 55.
Key Points to Remember
- Add/subtract 10: Change only the tens digit.
- Add 9: Add 10, subtract 1.
- Subtract 9: Subtract 10, add 1.
- Make a ten: Break the smaller number to reach the next ten, then add the rest.
- Add/subtract 20, 30, etc.: Change the tens digit by 2, 3, etc.
- Practice daily to get faster at mental maths.
Practice Problems
- Find 54 + 10 mentally.
- What is 78 − 10?
- Add 9 to 45 in your head.
- Subtract 9 from 71 mentally.
- Use the make-a-ten trick to find 38 + 5.
- Aman has ₹65. He gets ₹20 more. How much does he have?
Frequently Asked Questions
Q1. What is mental addition and subtraction?
It is doing addition and subtraction in your head without writing anything down. You use smart tricks to make the calculation easier.
Q2. How do I add 9 mentally?
Add 10 instead (which is easy), then subtract 1 to correct. Example: 46 + 9 = 46 + 10 − 1 = 55.
Q3. What is the make-a-ten strategy?
Break the number you are adding so that the first number reaches the next ten. Example: 28 + 5 = 28 + 2 + 3 = 30 + 3 = 33.
Q4. Why is mental maths important?
Mental maths helps you calculate quickly in daily life — at the shop, during games, or when checking answers. It also builds strong number sense.
Q5. Can I use mental maths for bigger numbers?
Yes, with practice. For larger numbers, you can still add or subtract 10, 20, 100, etc. mentally by changing only the relevant digit.
Q6. How can I practise mental maths at home?
Play number games: ask "What is 35 + 10?" during car rides, or count money at the shop. Daily 5-minute mental maths drills help a lot.
