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Year 10
Foundation

Checking and securing understanding of estimating through rounding

I can estimate the value of an expression through rounding.

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New
New
Year 10
Foundation

Checking and securing understanding of estimating through rounding

I can estimate the value of an expression through rounding.

Download all resources
Share activities with pupils

Lesson details

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.

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.

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.

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.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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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

Exit quiz

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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: $$108 cm^2$$, $$108$$