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Year 10 - Maths

Checking and securing understanding of rounding and truncating

Rounding, estimation and bounds

Unit Summary

This unit explores the impact of upper and lower bounds on additive and multiplicative calculations.

Lesson Summary

You will learn to estimate a value by rounding or truncating to a given degree of accuracy.

Key Notes

  • The first significant figure is the first non-zero digit to have place value.
  • Truncation does not consider the digits that follow in the value.
  • The loss of accuracy through rounding is not always bad.

Vocabulary To Learn

  • Round: Rounding means to change a number into another number that is approximately the same value but is easier to work with.
  • Degree of accuracy: A degree of accuracy shows how precise a number or measurement is. E.g to the nearest cm, nearest 10, 1 s.f., etc.
  • Significant figures: Significant figures are the digits in a number that contribute to the accuracy of the number. The first significant figure is the first non-zero digit.
  • Truncation: Truncation is when we simplifying a number by 'cutting off' one or more of the digits and replacing them with zeros if necessary to preserve place value.

Common Mistakes To Avoid

  • When truncating, pupils are tempted to round. Also, when truncating, they cut off the number without thinking about the magnitude.

3 Quick Questions (With Answers)

1. Solve this in steps: explain the method from this lesson and why each step matters.

The first significant figure is the first non-zero digit to have place value. Truncation does not consider the digits that follow in the value.

2. Use this key word in a maths sentence and explain it clearly. 'Round'

Rounding means to change a number into another number that is approximately the same value but is easier to work with. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: When truncating, pupils are tempted to round. Also, when truncating, they cut off the number without thinking about the magnitude. Correction: The use of the place value table shows the magnitude of the number, thus preserving their place value when truncating.

More Lessons In This Unit

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