Physics Lesson 1.3.3 - How to round up a number to the required number of significant figures?

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Welcome to our Physics lesson on How to round up a number to the required number of significant figures?, this is the third lesson of our suite of physics lessons covering the topic of Significant Figures and their Importance, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

How to round up a number to the required number of significant figures?

Suppose you measure the perimeter of a regular hexagon by and obtain the result P = 25.0 cm. The question requires you to calculate the side length of the hexagon. Thus, you make the following calculation:

It is obvious you cannot write the result in this way. You must round the result to fit the apparatus you have used to take the measurements. From the perimeter value, you can see the accuracy of apparatus is up to 0.1cm. This number has only one decimal place. Therefore, you must write the result at 1 decimal place as well. Hence, either you will write it as 4.1 cm or 4.2 cm. In this case, you must use the rounding rules, i.e. when the last digit is greater than 4, we have an increase in the rounded value. In the specific case, the last digit is 7, so we must write 4.2 cm for the size of the hexagon's side length.

You may wish to use the sig fig calculator to calculate significant figures and test some examples.

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6. Check your calculations for Units and Measurements questions with our excellent Units and Measurements calculators which contain full equations and calculations clearly displayed line by line. See the Units and Measurements Calculators by iCalculator™ below.
7. Continuing learning units and measurements - read our next physics tutorial: Units. Systems of Units. Fundamental and Derived SI Units

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