In this chapter, we explore 3-digit numbers further — learning how to add and subtract them with regrouping (carrying and borrowing). We also practise place value in hundreds, tens, and ones.
Quick Recap of Place Value
- Every digit in a 3-digit number has a place:
- Hundreds (H) – the leftmost digit.
- Tens (T) – the middle digit.
- Ones (O) – the rightmost digit.
In the number 346: H = 3, T = 4, O = 6.
So 346 = 300 + 40 + 6.
Adding 3-Digit Numbers with Regrouping
When the sum in ones is 10 or more, we carry 1 to the tens. When the sum in tens is 10 or more, we carry 1 to the hundreds.
Subtracting 3-Digit Numbers with Regrouping (Borrowing)
When the ones digit of the number being subtracted is larger, we borrow 10 from the tens. When the tens digit is smaller, we borrow from the hundreds.
Add 256 + 137.
Step 1 (Ones): 6 + 7 = 13. Write 3, carry 1.
Step 2 (Tens): 5 + 3 + 1 (carry) = 9. Write 9.
Step 3 (Hundreds): 2 + 1 = 3.
Answer: 393.
Add 468 + 275.
Step 1 (Ones): 8 + 5 = 13. Write 3, carry 1.
Step 2 (Tens): 6 + 7 + 1 = 14. Write 4, carry 1.
Step 3 (Hundreds): 4 + 2 + 1 = 7.
Answer: 743.
Subtract 542 - 318.
Step 1 (Ones): 2 - 8 not possible; borrow from tens. 12 - 8 = 4.
Step 2 (Tens): (4 - 1) - 1 = 2. (Tens reduced by 1 because we borrowed.)
Step 3 (Hundreds): 5 - 3 = 2.
Answer: 224.
Write the expanded form of 725.
725 = 700 + 20 + 5.
Answer: 700 + 20 + 5.
Compare 583 and 538.
Step 1: Same hundreds digit (5).
Step 2: Compare tens: 8 > 3.
Answer: 583 > 538.
Key Points
- Regroup (carry) when sum of a column is 10 or more.
- Borrow when the digit on top is smaller than the digit below in subtraction.
- Always start from the ones place.
Common mistakes
Never add or subtract hundreds with tens directly. Always align digits in their correct columns (H, T, O) before calculating.
Summary
3-digit numbers have hundreds, tens, and ones. Addition may need carrying; subtraction may need borrowing. Always work from right (ones) to left (hundreds).