Estimates on one side of the answer
A school collects ₹2,31,400 in term one and ₹4,67,850 in term two. Is the total more than 6 lakh?
- Two amounts to add.
- Round both down: 2,00,000 + 4,00,000 = 6,00,000. The total is more.
- Round both up: 3,00,000 + 5,00,000 = 8,00,000. The total is less.
- The total sits between 6 lakh and 8 lakh.
Yes. Rounding both amounts down to the lakh gives 6 lakh. The real total is more.
The rule
An estimate is an answer found with rounded numbers. The sum is the answer to an add. The difference is the answer to a take-away.
Rounding down never makes a number bigger. Rounding up never makes a number smaller. So we know which side of the answer the estimate is.
Round both numbers down: the estimate is never more than the sum. Round both up: it is never less than the sum. For a difference, round the first down and the second up. The estimate is never more than the difference.
| Job | Round | Estimate | The answer is |
|---|---|---|---|
| 7,82,300 − 3,15,200 | First down, second up | 3,00,000 | More than that |
| 7,82,300 − 3,15,200 | First up, second down | 5,00,000 | Less than that |
Round one up and one down. The estimate can be on either side.
Round each number up or down in the lab. See which side the estimate lands.
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