Learning Objectives
- Add numbers up to 3 digits with and without carrying
- Subtract numbers up to 3 digits with and without borrowing
- Solve word problems using addition and subtraction
- Check answers using reverse operations
Key Concepts
Addition (Giving Together)
When we add two numbers, we put them together to get a bigger number. Start adding from the ones place, then move to the tens place, and then the hundreds place. If the sum of digits in any place is 10 or more, carry the extra to the next place. For example, 156 + 278 = 434.
Subtraction (Taking Away)
When we subtract, we take away one number from another. Start subtracting from the ones place. If the top digit is smaller than the bottom digit, borrow 1 from the next place. For example, in 432 - 178, we cannot take 8 from 2, so we borrow from the tens place.
Word Problems
Word problems tell a story with numbers. Look for clue words: "total", "altogether", "in all", and "sum" mean addition. Words like "left", "remaining", "difference", and "how many more" mean subtraction. Read the problem carefully before solving!
Checking Your Answer
You can check subtraction by adding: if 500 - 236 = 264, then 264 + 236 should equal 500. You can check addition by subtracting: if 145 + 233 = 378, then 378 - 233 should equal 145.
Important Terms
- Addition: Putting two or more numbers together to get a total
- Subtraction: Taking one number away from another to find the difference
- Carry Over: Moving extra value to the next place when a column adds up to 10 or more
- Borrowing: Taking 1 from the next place when the top digit is too small to subtract
- Sum: The answer you get when you add numbers
- Difference: The answer you get when you subtract numbers
Quick Revision
- Always start adding or subtracting from the ones place (right side)
- Carry over when the sum in a column is 10 or more
- Borrow from the next place when you cannot subtract
- Check addition with subtraction and subtraction with addition
- Read word problems carefully and look for clue words