Topic 2
Sample content
Estimating and rounding
Think about it
You have ₹500. In the shop you pick items costing ₹98, ₹149 and ₹212. Without exact adding, can you tell quickly if you have enough?
The idea
Estimating means finding a number close enough to be useful. Rounding helps: look at the digit to the right of the place you are rounding to. If it is 5 or more, round up; otherwise round down.
Worked example
- 1Round each price to the nearest ten: ₹98 → ₹100, ₹149 → ₹150, ₹212 → ₹210
- 2Add the rounded values: 100 + 150 + 210 = ₹460
- 3₹460 is less than ₹500, so you have enough
- 4Exact total is ₹459, very close to the estimate
Rounding to the nearest hundred
| Number | Tens digit | Rounded |
|---|---|---|
| 342 | 4 (less than 5) | 300 |
| 351 | 5 (5 or more) | 400 |
| 1,287 | 8 | 1,300 |
Activity · Shopping challenge
Next time you shop with family, estimate the bill before reaching the counter. Compare your estimate with the real bill. How close were you?
Key takeaways
- Estimation gives a quick, close answer
- 5 or more rounds up; less than 5 rounds down
- Rounding first makes mental adding easy
- Check estimates against exact answers