Ones: 2 < 7, so regroup: 52 = 40 + 12, then 12 - 7 = 5, 4 - 1 = 3, answer: 35
Ones: 4 < 8, so regroup: 64 = 50 + 14, then 14 - 8 = 6, 5 - 2 = 3, answer: 36
Ones: 3 < 9, so regroup: 73 = 60 + 13, then 13 - 9 = 4, 6 - 4 = 2, answer: 24
Ones: 1 < 6, so regroup: 81 = 70 + 11, then 11 - 6 = 5, 7 - 5 = 2, answer: 25
Ones: 5 < 8, so regroup: 95 = 80 + 15, then 15 - 8 = 7, 8 - 6 = 2, answer: 27
Ones: 4 < 7, regroup from tens (0), regroup from hundreds: 304 = 200 + 90 + 14, then 14 - 7 = 7, 9 - 2 = 7, 2 - 1 = 1, answer: 177
Ones: 0 < 8, regroup from tens (0), regroup from hundreds: 400 = 300 + 100 = 300 + 90 + 10, then 10 - 8 = 2, 9 - 5 = 4, 3 - 1 = 2, answer: 242
Ones: 3 < 6, regroup from tens (0), regroup from hundreds: 503 = 400 + 100 + 3 = 400 + 90 + 13, then 13 - 6 = 7, 9 - 4 = 5, 4 - 2 = 2, answer: 257
Ones: 0 < 7, regroup from tens (0), regroup from hundreds: 600 = 500 + 100 = 500 + 90 + 10, then 10 - 7 = 3, 9 - 8 = 1, 5 - 3 = 2, answer: 213
Ones: 5 < 9, regroup from tens (0), regroup from hundreds: 705 = 600 + 100 + 5 = 600 + 90 + 15, then 15 - 9 = 6, 9 - 2 = 7, 6 - 4 = 2, answer: 276
Place Value: The value of a digit based on its position in a number (ones, tens, hundreds, etc.)
Regrouping: Converting 1 unit from a higher place value to 10 units of the next lower place value
Borrowing: Another term for regrouping in subtraction operations
Base-Ten System: Our number system where each place value is 10 times the previous one
Worksheet: A collection of practice problems designed to reinforce specific mathematical concepts
Regrouping Rule: When the bottom digit is larger than the top digit in a place value, you must regroup from the next higher place value
Value Conversion: 1 hundred = 10 tens, 1 ten = 10 ones
Subtraction Sequence: Always start from the rightmost digit (ones place) and move left
Zero Handling: When you encounter a zero and need to regroup, continue to the next non-zero place value
Practice Principle: Repetition with varied difficulty levels leads to mastery
- Align Numbers: Write the numbers vertically with place values aligned
- Start from Right: Begin subtraction in the ones place
- Check Need: Compare digits in each place value (bottom vs top)
- Regroup if Needed: If bottom digit is larger, borrow from next higher place
- Subtract Digit: Perform subtraction in that place value
- Move Left: Continue to next place value (tens, then hundreds)
- Combine Results: Write the final answer combining all place values
- Verify: Add the difference back to the subtracted number to check accuracy
Simple Example: \(42 - 15\)
Ones: \(2 < 5\), so regroup: \(42 = 30 + 12\), then \(12 - 5 = 7\), \(3 - 1 = 2\), answer: \(27\)
Intermediate Example: \(203 - 147\)
Ones: \(3 < 7\), regroup from tens (but tens is 0), so regroup from hundreds: \(203 = 100 + 100 + 3 = 100 + 90 + 13\), then \(13 - 7 = 6\), \(9 - 4 = 5\), \(1 - 1 = 0\), answer: \(56\)
Complex Example: \(500 - 289\)
Ones: \(0 < 9\), regroup from tens (0), regroup from hundreds: \(500 = 400 + 100 = 400 + 90 + 10\), then \(10 - 9 = 1\), \(9 - 8 = 1\), \(4 - 2 = 2\), answer: \(211\)
Tips:
- Always start subtracting from the ones place
- Draw lines to separate place values visually
- Check your answer by adding the difference back to the subtracted number
- Practice with base-ten blocks to visualize the process
- When you see a zero, always check if regrouping is needed from higher places
Common Mistakes:
- Forgetting to regroup when needed
- Subtracting smaller number from larger regardless of position
- Misaligning digits when writing numbers vertically
- Forgetting to reduce the higher place value after borrowing
- Not continuing regrouping when there are zeros in higher places
Memory Aids:
- "More on the floor, go next door" - when bottom number is bigger, borrow from next place
- "1 hundred = 10 tens = 100 ones" - know these conversions
- Always start from the right (ones place)
- After borrowing, the higher place value decreases by 1
- Check your work: Difference + Subtracted = Original number
250 - 87: Ones: 0 < 7, regroup from tens (5 becomes 4), 10 - 7 = 3, tens: 4 < 8, regroup from hundreds (2 becomes 1), 14 - 8 = 6, hundreds: 1 - 0 = 1, answer: 163 seashells
305 - 168: Ones: 5 < 8, regroup from tens (0), regroup from hundreds: 305 = 200 + 100 + 5 = 200 + 90 + 15, then 15 - 8 = 7, 9 - 6 = 3, 2 - 1 = 1, answer: 137 stickers
400 - 237: Ones: 0 < 7, regroup from tens (0), regroup from hundreds: 400 = 300 + 100 = 300 + 90 + 10, then 10 - 7 = 3, 9 - 3 = 6, 3 - 2 = 1, answer: 163 books
502 - 346: Ones: 2 < 6, regroup from tens (0), regroup from hundreds: 502 = 400 + 100 + 2 = 400 + 90 + 12, then 12 - 6 = 6, 9 - 4 = 5, 4 - 3 = 1, answer: $156
600 - 429: Ones: 0 < 9, regroup from tens (0), regroup from hundreds: 600 = 500 + 100 = 500 + 90 + 10, then 10 - 9 = 1, 9 - 2 = 7, 5 - 4 = 1, answer: 171 apples
No regrouping needed: 8 - 3 = 5, 7 - 2 = 5, answer: 55
Ones: 4 < 8, regroup: 94 = 80 + 14, then 14 - 8 = 6, 8 - 5 = 3, answer: 36
Ones: 0 < 5, regroup from tens (0), regroup from hundreds: 200 = 100 + 100 = 100 + 90 + 10, then 10 - 5 = 5, 9 - 4 = 5, 1 - 1 = 0, answer: 55
No regrouping needed: 3 - 1 = 2, 6 - 2 = 4, answer: 42
Ones: 7 < 8, regroup from tens (0), regroup from hundreds: 407 = 300 + 100 + 7 = 300 + 90 + 17, then 17 - 8 = 9, 9 - 9 = 0, 3 - 1 = 2, answer: 209