Year 8 - Maths
Overestimating vs underestimating
Estimation and rounding
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit helps pupils understand rounding to different decimal places, and significant figures. Pupils will also learn how to truncate numbers and understand the contexts in which these skills are useful. The unit ends will an exploration of rounding and inequality errors.
Lesson Summary
You will learn to determine whether calculations using rounding or truncating will give an underestimate or overestimate.
Key Notes
- When multiplying or adding, using a value which has been rounded up results in an overestimate.
- When dividing or subtracting, using a value which has been rounded up results in an under or overestimate.
- Calculations using rounding or truncating will give an over or underestimate.
- By careful consideration of the calculation, it is possible to tell if an answer is an over or underestimate.
Vocabulary To Learn
- Overestimate: An overestimate is an estimate for a calculation which is greater than the exact answer.
- Underestimate: An underestimate is an estimate for a calculation which is less than the exact answer.
Common Mistakes To Avoid
- When subtracting or dividing, the largest value is found by subtracting or dividing the largest rounded number by the largest rounded divisor or additive inverse.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
When multiplying or adding, using a value which has been rounded up results in an overestimate. When dividing or subtracting, using a value which has been rounded up results in an under or overestimate.
2. Use this key word in a maths sentence and explain it clearly. 'Overestimate'
An overestimate is an estimate for a calculation which is greater than the exact answer. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: When subtracting or dividing, the largest value is found by subtracting or dividing the largest rounded number by the largest rounded divisor or additive inverse. Correction: Drawing a number line to show the subtraction of the smallest number will help students see how to achieve an overestimate or underestimate. When using division, reiterating the division of number is the same as multiplying by its reciprocal.
More Lessons In This Unit
- Checking by estimating Study Guide
- Checking understanding of rounding Study Guide
- Degrees of accuracy Study Guide
- Estimating numerical calculations Study Guide
- Inequality notation to express error Study Guide
- Problem solving with estimation and rounding Study Guide
- Rounding decimals to significant figures Study Guide
- Rounding errors Study Guide
- Rounding integers to one significant figure Study Guide
- Rounding integers to significant figures Study Guide
- Rounding to any number of decimal places Study Guide
- Rounding to three decimal places Study Guide
- Securing understanding of rounding Study Guide
- Truncating Study Guide
- Using inequality notation for errors in calculations Study Guide
Browse all guides in the Year 8 Maths guide library.