Estimate whether an answer is reasonable

Reasonableness checking involves judging whether an addition or subtraction result has the expected size and direction, using relationships among numbers, benchmark amounts such as 10 and 20, and representations such as number lines or ten-frames. For quantities within 100, a learner can identify answers that are too large, too small, or inconsistent with the situation, recognizing that addition generally increases a quantity and subtracting a smaller number decreases it; formal rounding and estimation with larger or more complex numbers are beyond this scope.

Detailed Explanation: Estimate whether an answer is reasonable

To check whether an answer is reasonable, ask:

Should the answer get bigger or smaller?
- Addition usually makes a number bigger.
- Subtraction usually makes a number smaller.
What answer would make sense? Use a nearby benchmark, such as $10$ or $20$ , to think about the size.

Example

Mia has $18$ stickers. She gets $7$ more. She says she has $25$ stickers now. Is her answer reasonable?

This is addition, so the answer should be greater than $18$ .
Think of $18$ as close to $20$ . Then $20+7$ is about $27$ .
The answer $25$ is close to $27$ and is greater than $18$ .

So, $25$ is a reasonable answer.

Learn by doing: Estimate whether an answer is reasonable

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Addition - Estimate Sum - 2 & 2 Digit

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