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      Checking and securing understanding of estimating through rounding

      Lesson details

      Learning outcome

      I can estimate the value of an expression through rounding.

      Key learning points

      1. Rounding to 1 significant figure allows quick estimation with the magnitude of the estimation being close.
      2. The estimation will be closer to the true answer the less rounding you do.
      3. Estimating through rounding is meant to be quick and easy, taking too long defeats the purpose.

      Keywords

      • Estimate - A quick estimate for a calculation is obtained from using approximate values, often rounded to 1 significant figure.

      • Significant figure - 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.

      • Overestimate - An estimate for a calculation which is greater than the exact answer.

      • Underestimate - An estimate for a calculation which is less than the exact answer.

      Common misconception

      Assuming all zero digits are not significant.

      Relate significance back to the communication of accuracy and that some digits are significant as they preserve the place value of other digits.

      Teacher tip

      Give the pupils a similar approximation to the one on slide 20. Ask them to work on MWBs and show their answers. Choose some different approaches to discuss and talk about the pros and cons of each and what an exam question would require.

      Licence

      This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0
      except where otherwise stated. See Oak's terms & conditions
      (Collection 2).

      Lesson video

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      Prior knowledge starter quiz

      6 Questions

      Q1.
      Rounding means to change a number into another number that is the same value but is easier to work with.

      Correct Answer: approximately, nearly, approximate, almost, roughly

      Q2.
      Round 780 257 to the nearest ten thousand.

      Correct Answer: 780 000, 780000

      Q3.
      Round 123.408 to 2 decimal places.

      Correct Answer: 123.41

      Q4.
      Round 0.01872 to 2 significant figures.

      Correct Answer: 0.019

      Q5.
      Truncate 74 283 to 2 significant figures.

      Correct Answer: 74 000, 74000

      Q6.
      Truncate 0.02078 to 3 significant figures.

      Correct answer: 0.020
      0.0207
      0.0208
      0.021

      6 Questions

      Q1.
      When estimating calculations round each value to 1 figure.

      Correct Answer: significant

      Q2.
      Choose the correct calculation to estimate the cost of hiring a plumber for 5.75 hours, where the total cost = £48 × number of hours + £32

      £50 × 5 + £30
      £40 × 5 + £30
      Correct answer: £50 × 6 + £30
      £50 × 6 + £32
      £48 × 6 + £30

      Q3.
      Estimate the value of $$7.236\times38.4\over1.704$$

      Correct Answer: 140

      Q4.
      Will the estimation of 45.87 × 763 be an overestimate or underestimate?

      Correct Answer: overestimate

      Q5.
      Estimate the total length of 23 bricks if each brick measures 21.5 cm.

      Correct Answer: 400 cm, 400cm, 400

      Q6.
      Estimate the area of a circle with a diameter of 12.8 cm.

      Correct Answer: $$108 cm^2$$, $$108$$

      To help you plan your 10 maths lesson on: Checking and securing understanding of estimating through rounding, download all teaching resources for free and adapt to suit your pupils' needs...