# Rules of Significant Figures

Now that we’ve covered scientific, engineering, and decimal notation, it’s time to learn the rules of significant figures (abbreviated SF, and also referred to as significant digits). Without knowing these rules, you will NOT be able to add, subtract, multiply, or divide any number correctly moving forward. The first video will walk you through how to count for the correct number of significant digits in any type of number:

Next, you’ll need to know the rules for rounding numbers to the correct number of significant figures. Rounding and significant figures go hand-in-hand in almost every calculation. When you’re asked to calculate something to the correct number of SF’s, it implies that you round as well. Also, don’t assume you know the rules, because what you learned in elementary school no longer applies here the same way, especially when your last significant figure is a 5.

Now that you now the rules of counting and rounding SF’s, let’s trying adding, subtracting, multiplying, or dividing numbers.

Part 2 of this series shows more of the same, except we extend our understanding to numbers of greater complexity, such as the operations applied to scientific notation numbers.

A few things to keep in mind when operating with numbers in scientific notation are summarized underneath. Of course, most scientific calculators – namely the one recommended for this course – enables you to find the answer without the recommendations below.

Tips for Adding and Subtracting Scientific Numbers

If two or more numbers to be added or subtracted have the same power of 10, we combine the numbers and keep the same power of 10.  For example: null

If the powers of 10 are different, they must be made equal before the numbers can be combined.

• A shift of the decimal point of one place to the left will increase the exponent by 1.
• A shift of the decimal point of one place to the right will decrease the exponent by 1.

For example:

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