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Class 3
Chapter 9: House of Hundreds — II
When ones or tens add up to 10 or more, we 'carry' to the next column. Estimating first gives a rough answer so you can check whether the exact answer makes sense.
Learning outcomes
- Add and subtract three-digit numbers with regrouping
- Estimate before computing
Activities
- Estimate-then-check sums
Worked examples
Read through these first, then try the practice below.
Example 1 — Estimate then add
Estimate 198 + 305 by rounding to the nearest hundred. Then find the exact sum.
Solution: Rounded: 200 + 300 = 500. Exact: 198 + 305 = 503. The estimate is close.
Example 2 — Subtract with regrouping
Find 405 − 178.
Solution: Borrow from the tens, then from the hundreds. 405 − 178 = 227.
Self-do practice
Question 1 of 3 · Score 0/0Find 256 + 187.
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