🔵Adding & Subtracting Large Numbers
Add and subtract large numbers the same way as small ones — line up the place values and work from the right, carrying (in addition) or borrowing (in subtraction) when needed.
Example: 3,456 + 2,789 → add ones, tens, hundreds, thousands, carrying each time, to get 6,245.
👀 See a worked example
Add 3,456 + 2,789.
Carry through each column: 6,245.
Subtract 5,000 − 1,250.
Borrow across the zeros: 3,750.
🤖 Vidi's Key Points
- Line up place values; work from the right.
- Carry when a column makes 10 or more; borrow when the top is smaller.
- The method is the same for big numbers as for small ones.
🟢Estimating & Word Problems
Estimating means rounding first to get a quick, close answer. Round each number to the nearest 100 or 1000, then add or subtract.
In word problems, total / altogether / in all mean add; left / difference / how many more mean subtract. You can check your exact answer against your estimate.
👀 See a worked example
Estimate 298 + 503 by rounding to the nearest 100.
300 + 500 = 800 (exact is 801).
A library had 4,500 books and bought 1,250 more. How many now?
'More' total → 4,500 + 1,250 = 5,750 books.
🤖 Vidi's Key Points
- Estimate by rounding before you calculate.
- 'Total/altogether' → add; 'left/difference' → subtract.
- Use the estimate to check your exact answer is sensible.
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