🔵What is Regrouping (Borrowing)?
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.
👀 See a worked example
Subtract 52 − 18.
- Ones: 2 − 8 can't be done → borrow: 12 − 8 = 4 (tens become 4).
- Tens: 4 − 1 = 3.
So 52 − 18 = 34.
Subtract 305 − 47.
- Ones: 5 − 7 can't be done → borrow from tens. But tens are 0, so borrow from hundreds first: 3 hundreds → 2 hundreds and 10 tens; then 10 tens → 9 tens and the ones become 15.
- Ones: 15 − 7 = 8; Tens: 9 − 4 = 5; Hundreds: 2.
So 305 − 47 = 258.
🤖 Vidi's Key Points
- Borrowing is needed when the top digit is smaller than the bottom digit.
- Borrow 1 from the next column on the left — it is worth 10 in the column you need.
- Subtract from right to left: ones, then tens, then hundreds.
🟢Subtraction Word Problems & Checking
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. ✔️
👀 See a worked example
Meena had ₹85 and spent ₹47. How much is left?
"Left" means subtract: 85 − 47 = ₹38. Check: 38 + 47 = 85 ✔️
A tank had 200 litres; 65 litres were used. How much remains?
200 − 65 = 135 litres.
🤖 Vidi's Key Points
- Words like 'left', 'remaining', 'difference' and 'fewer' mean subtract.
- Check subtraction by adding the answer to the number you took away.
- It should give back the number you started with.
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