Number Sense & Estimation
Numbers carry magnitude and structure; estimation and reasonableness can reveal what an exact answer should look like before calculation.
What you'll learn
- Estimate products by replacing awkward factors with nearby friendly numbers.
- Use bounds and place value to reject impossible results.
- Decide when an estimate settles a question and when exact calculation is still needed.
- Transfer estimation to a rate and unit-conversion setting.
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Worked recap: Estimate before calculating
For 198 × 5, estimate with 200 × 5 = 1000. The exact product should be slightly smaller.
Subtract the two extra groups of five: 1000 − 10 = 990. The estimate helps you catch an answer with the wrong size.