What Are the Common Rules When Adding Significant Figures?

By Staff WriterLast Updated March 24, 2020

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When adding numbers, the rules of significant figures dictate that the sum should be rounded to the same place as the least significant place of the number, with the least number of places after the decimal point. Significant figures are important when recording and relaying scientific data because they provide the reader with an idea of how best one can report/measure data.

For example, if 12.2, 3.66, 214.39 and 2.472 are to be added, the answer would be 232.7 because the number with least decimal places is 12.2 meaning the answer should be rounded to 0.1 decimal place. Other rules include:

Any non-zero number is significant

Any zeros in the middle of two significant numbers are significant

Trailing zeros or final zeros in the decimal portion are significant.