Addition and Subtraction with Carrying and Borrowing: Class 3 Study Guide
Adding combines amounts and subtracting finds the difference or what is left. Regrouping makes both work for bigger numbers.
Addition and subtraction are related. If 125 + 237 = 362, then 362 − 237 = 125. This idea helps you check work: after you add, subtract one number from the answer to see if you get the other.
For bigger numbers write them in columns: ones under ones, tens under tens and hundreds under hundreds. Start from the right, which is the ones column.
Addition with carrying
When the digits in a column add up to 10 or more, write the ones digit and carry the tens digit to the next column.
Line up ones, tens and hundreds.
8 + 4 = 12. Write 2, carry 1 ten.
5 + 6 + 1 = 12. Write 2, carry 1 hundred.
2 + 1 + 1 = 4. The sum is 422.
Subtraction with borrowing
If the top digit is smaller than the bottom digit, borrow 1 from the next column to the left. That 1 ten becomes 10 ones.
Top number first.
3 is less than 7. There are no tens to borrow, so borrow from the hundreds: 5 hundreds becomes 4 hundreds and 10 tens. Then borrow 1 ten: 9 tens and 13 ones. 13 − 7 = 6.
9 − 6 = 3.
4 − 2 = 2. The answer is 236.
Word problems
Look for words that tell the operation. Total, altogether, in all, sum point to addition. Left, fewer, difference, remain, how many more point to subtraction. Example: A shop had 365 notebooks and sold 148. How many are left? 365 − 148 = 217.
| Problem | Operation | Answer |
|---|---|---|
| Ria has 127 beads and gets 95 more. | 127 + 95 | 222 |
| A train has 480 seats; 356 are filled. | 480 − 356 | 124 empty |
Checking and common mistakes
Check addition by subtracting and subtraction by adding. Common mistakes: forgetting to add the carried number, subtracting the smaller digit from the larger regardless of position, and writing digits in untidy columns. In money problems, remember to write the unit (₹) in the answer.
Check your understanding: model answers
1. 349 + 276 = 625. 2. 600 − 238 = 362. 3. 482 + 459 = 941 students.
✨ Key Takeaways
- Carry when a column makes 10 or more; borrow when the top digit is too small.
- Always work from the ones column.
- Addition and subtraction are inverse operations, so use one to check the other.
- Estimating first catches big errors.
💬 Questions for Discussion & Reflection
- Find 349 + 276.
- Find 600 − 238.
- A school has 482 boys and 459 girls. How many students are there in all?