Course summary field: Master carrying, borrowing (even across zeros), and how to double-check your work.
You already know how to add and subtract. This unit is about handling the tricky moments: when columns don’t have enough room, or when you have to “break open” a zero.
Regrouping in addition (carrying): When a column adds up to 10 or more, you can’t fit that in one spot. So you write down the ones digit and carry the leftover ten into the next column.
Example 1:
Ones column: 8 + 7 = 15 → write 5, carry the 1
Tens column: 1 (carried) + 5 + 6 = 12 → write 2, carry the 1
Hundreds column: 1 (carried) + 4 + 2 = 7
Answer: 725
Regrouping in subtraction (borrowing): When the top digit is smaller than the bottom digit, you borrow 1 ten (or hundred, etc.) from the column to the left.
Example 2:
Ones column: 2 − 8. Can’t do it! Borrow from the tens column: the 4 becomes 3, and the 2 becomes 12. Now 12 − 8 = 4.
Tens column: 3 − 6. Still can’t do it! Borrow from the hundreds column: the 5 becomes 4, and the 3 becomes 13. Now 13 − 6 = 7.
Hundreds column: 4 − 1 = 3
Answer: 374
Borrowing across a zero is the trickiest version. Like 500 − 187. You can’t borrow from a 0, so you have to reach one column further left.
Example 3:
Ones column: 2 − 8. Can’t do it! Borrow from the tens column: the 4 becomes 3, and the 2 becomes 12. Now 12 − 8 = 4.
Tens column: 3 − 6. Still can’t do it! Borrow from the hundreds column: the 5 becomes 4, and the 3 becomes 13. Now 13 − 6 = 7.
Hundreds column: 4 − 1 = 3
Answer: 374
⚡Quick Tip: Always check your subtraction by adding. If you got 313 for 500 − 187, check it: 313 + 187 should equal 500. (It does! ✅)
Cant believe we’re done with Unit 2 this quick! For more practice solve lesson 1, 4 and 9 from our booklet.