🔢 Subtraction with Regrouping

Sometimes the top digit is smaller than the bottom digit, so we cannot subtract directly. We regroup (also called borrowing): take 1 from the next column on the left, which is worth 10 in the column we need.
Example: in 42 − 7, we cannot do 2 − 7. So borrow 1 ten from the tens: the 2 becomes 12, and the 4 tens become 3. Now 12 − 7 = 5, and the tens are 3 → answer 35.
Subtract from right to left: ones first, then tens, then hundreds.

In a word problem, words like left, remaining, how many more, difference, fewer tell you to subtract.
Check your answer with addition: the answer plus the number you took away should give back the start. If 52 − 18 = 34, then 34 + 18 should equal 52. ✔️