Adding and Subtracting Two-Digit Numbers: Class 2 Study Guide
Two-digit addition and subtraction use place value. When ones add up to more than 9, we regroup.
Write the numbers one below the other, with tens under tens and ones under ones. Add the ones first, then the tens. When the ones make 10 or more, carry a ten to the tens column. In subtraction, if the top ones digit is smaller, borrow one ten, which becomes ten ones.
Children who understand regrouping can explain why they carry or borrow. Using bundles of sticks or beads helps to show that 1 ten really is 10 ones.
Addition with carrying
To add 38 + 25: ones 8 + 5 = 13, so write 3 and carry 1 ten. Tens: 3 + 2 + 1 = 6. The answer is 63.
8 + 5 = 13. Write 3, carry 1.
3 + 2 + the carried 1 = 6.
63.
63 − 25 = 38.
Subtraction with borrowing
To subtract 52 − 27: the ones 2 are less than 7, so borrow a ten from 5 tens. Now there are 4 tens and 12 ones. 12 − 7 = 5 ones and 4 − 2 = 2 tens. The answer is 25.
| Problem | Without regrouping | With regrouping |
|---|---|---|
| Add | 23 + 14 = 37 | 38 + 25 = 63 |
| Subtract | 56 − 23 = 33 | 52 − 27 = 25 |
Word problems
Look for clue words. In all, altogether, total, sum mean add. Left, difference, how many more, fewer mean subtract. Example: A school library had 48 books and received 35 more. 48 + 35 = 83 books. If 27 are lent out, there are 83 − 27 = 56 left.
Worked examples and common mistakes
Example: 46 + 37 = 83. Example: 70 − 38 = 32 (borrow from the 7 tens). Common mistakes: forgetting to add the carried ten, subtracting the smaller digit from the larger in every column and not lining up the digits. Draw columns on squared paper to keep digits tidy.
Check your understanding: model answers
1. 47 + 28 = 75. 2. 63 − 29 = 34. 3. 56 − 18 = 38 mangoes.
✨ Key Takeaways
- Add or subtract the ones first.
- Carry a ten when ones make 10 or more; borrow a ten when ones are too small.
- Check addition with subtraction.
- Estimate to check your answer.
💬 Questions for Discussion & Reflection
- Find 47 + 28.
- Find 63 − 29.
- There are 56 mangoes. 18 are sold. How many are left?