An informal estimate of a sum is a nearby, easier total found by using place-value structure, such as replacing two-digit addends with the nearest tens or choosing compatible numbers. The estimate should preserve the sum’s approximate size, allow a student to judge whether an exact answer is reasonable, and may be recognized as above or below the actual total; it is not the exact sum. More formal estimation with larger numbers, decimals, or general error bounds is not included.
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Detailed Explanation: Estimate sums informally
An estimate is a nearby answer that is easier to find. It is not the exact sum.
To estimate a sum:
- Look at the tens in each number.
- Round each number to the nearest ten.
- Add the rounded numbers.
Example: Estimate .
- is close to .
- is close to .
- Add the easier numbers:
So, the estimated sum is about .
The exact sum is , so is a reasonable estimate and is close to the actual answer.
Learn by doing: Estimate sums informally
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Practice:
Addition - Estimate Sum - 2 & 2 Digit
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This Worksheet Includes:
- Addition - Estimate Sum - 2 & 2 Digit
- Addition - Estimate Sum - 3 & 2 Digit
- Addition - Whole Number 2 digit + 2 digit, No Carry
- Base 10 Blocks - Adding - Picture to Answer, No Carry - Tens and Ones
- Base 10 Blocks - Counting - Picture to Number - Tens and Ones
- Addition - Whole Number 1 digit + 1 digit, No Carry
- Ten Groups - Add, Without Carry, Less than 10
- Ten Groups - Add, Without Carry, Less than 20
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