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### Mass Percent Composition

Posted: **Tue Oct 02, 2018 12:54 pm**

by **Nada AbouHaiba 1I**

When it comes to finding the mass percent composition of a substance how many sig figs should we round to? Or is there a certain amount of decimal places we need to round to? Or does it not make a difference? I've noticed that in the textbook solution they'll usually do up to two decimal places, but I've also seen them do up to four.

Thank you!

### Re: Mass Percent Composition

Posted: **Tue Oct 02, 2018 1:04 pm**

by **Ray Guo 4C**

Should use significant figures instead of decimal places because finding the mass percent composition uses division. The number of significant figures in your answer should be the same as that of the value with the least significant figures that you use in the calculation.

### Re: Mass Percent Composition

Posted: **Tue Oct 02, 2018 1:20 pm**

by **Kelly Hollman**

Use the smallest amount of sig figs you find in the given numbers. For example, if you are given 20.0 grams and 156.6 grams, you'd use three sig figs in your answer (20.0 has three, 156.6 has four.)

### Re: Mass Percent Composition

Posted: **Tue Oct 02, 2018 2:00 pm**

by **Diviya Khullar 1G**

In this calculation you are typically multiplying or dividing, and the rule when it comes to significant figures in multiplication or division the rule is that your answer should have the same number of significant figures as the factor with the least number of significant figures. And also make sure you are rounding up or down as needed. For example, if you are multiplying 2.05 (a number with 3 significant figures) and 3.7 (a number with 2 significant figures), you would have to write your answer with 2 significant figures. Your answer would be 7.6.

### Re: Mass Percent Composition

Posted: **Tue Oct 02, 2018 2:27 pm**

by **anishathomas**

Hi yeah you just have to use the least amount of sig figs and I usually wait till the end to do so just because itâ€™s less of a hassle doing it in between problems. However there are different rules between multiplying numbers and finding dog figs than if you were adding numbers which I would just review looking at a khan academy video.