Consider three masses that you wish to add together: 3 g. 1.4 g, and 3.3 g. These numbers represent measured values. How do you add the numbers together and report your answer to the correct number of significant figures?

1 Answer
Sep 2, 2016

The answer is #"8 g"#.


When adding or subtracting, the result should be rounded to the same number of decimal places as the number in the problem with the fewest decimal places.

#"3 g"+"1.4 g"+"3.3 g"="7.7 g"#

However, #"3 g"# is a whole number with no decimal places, so #"7.7 g"# should be rounded to the whole number #8#.

Therefore, #"3 g"+"1.4 g"+"3.3 g"="8 g"#

This illustrates the importance of recording measurements so that you record what you can read exactly from the instrument, plus one estimated digit.

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