When should you round the numbers to take significant figures into account?

Here is the pattern we try to follow on all of our solutions. If all of the math operations are the same, i.e. all multiplication/division or all addition/subtraction, then we will not round until the very end of the calculations. If the math operations switch, i.e. switches from multiplication to addition, then we will round before the switch and then also at the end when the answer is obtained.

In an equation like this:

(100.0) x (1.00) x (34.5-34.4)

You do the subtraction first, then use the rules of addition and subtraction to report your answer to the tenths place:

(100.0) x (1.00) x (0.1)

Then you multiply all three numbers and round after that. Since the 0.1 has only one significant figure, your answer can have only one.

Some equations will have special rules about rounding (Celsius to Fahrenheit, for example) so pay close attention to the text when it is first describing how to use a particular equation.

Your answers need not be IDENTICAL to the given answers to be correct. They need to have the right number of significant figures, but the last digit can be off compared to the given answer. Remember, the last significant figure has error in it. Minor differences between answers reflect that error.

Tags: Chemistry, Math, Physics, Significant Figures
Last update:
2019-01-29 20:54
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