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Rounding and estimation
Scientific calculators are a wonderful invention, but they're only as good as the...
Scientific calculators are a wonderful invention, but they're only as good as the people who use them. If you often get an unexpected – or ridiculous – result when you press the ‘enter’ button, this unit is for you. Learn how to do a calculation correctly and get the right answer every time.
By the end of this unit you should be able to:
- round a given whole number to the nearest 10, 100, 1000 and so on;
- round a decimal number to a given number of decimal places or significant figures;
- use rounded numbers to find rough estimates for calculations;
- use a calculator for decimal calculations involving +, −, × and ÷, giving your answer to a specified accuracy (e.g. decimal places or significant figures) and checking your answer by finding a rough estimate;
- check your answers to calculations by ensuring that the correct calculation has been done, in the correct order;
- check your answers by checking that the units are consistent;
- check your answers by checking the result against a rough estimate;
- check your answers by checking that the answer makes sense in the context of the problem.
- Current section: Introduction
- Learning outcomes
- 1 Rounding
- 1.1 Rounding in daily life
- 1.2 Rounding whole numbers
- 1.3 Rounding in general
- 1.4 Rounding decimals
- 1.5 Significant figures
- 1.6 Significant figures for numbers less than one
- 2 Estimation
- 3 Checking your answers
- 3.1 Have I done the right calculation?
- 3.2 Have I used the correct order for my calculation?
- 3.3 Have I given due consideration to units of measurement?
- 3.4 Did I make a rough estimate to act as a check?
- 3.5 Does the answer make sense in the real world?
- 3.6 Additional practice
- 4 OpenMark quiz
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Rounding and estimation
For many calculations you use a calculator. The main aim of this unit is to help you to do this in a sensible and fruitful way. Using a calculation to solve a problem involves four main stages:
Stage 1: working out what calculation you want to do;
Stage 2: working out roughly what size of answer to expect from your calculation;
Stage 3: carrying out the calculation;
Stage 4: interpreting the answer – Does it agree with the rough estimate? Does it make sense in terms of the original problem?
This unit focuses on Stages 2 and 4.
This unit is from our archive and is an adapted extract from Open mathematics (MU120) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore other courses we offer in.
This is an extract from an Open University course which is no longer available to new students. If you found this interesting you could explore more free Mathematics Education courses or view the range of currently available OU Mathematics Education courses.
Copyright & revisions
Originally published: Friday, 10th June 2011
- Creative-Commons: The Open University is proud to release this free course under a Creative Commons licence. However, any third-party materials featured within it are used with permission and are not ours to give away. These materials are not subject to the Creative Commons licence. See terms and conditions. Full details can be found in the Acknowledgements section.
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