Calculating Sig Figs

Bryan Ramirez 2C
Posts: 2
Joined: Fri Sep 28, 2018 12:17 am

Calculating Sig Figs

When multiplying/dividing and adding/subtracting with sig figs how do you know which value you’ll have to round to in order to get your final answer?

Posts: 60
Joined: Tue Nov 28, 2017 3:02 am

Re: Calculating Sig Figs

Generally, just look at the amount of sig figs of each value and then round to the nearest number according to the lowest number of sig figs (to be less precise). For example, when dividing 3.04 mol by 1.2 L to get a molarity of 2.5M instead of 2.53M. Since 1.2L is two sig figs the answer must be also at two sigs figs.

Julia Lee
Posts: 80
Joined: Fri Sep 28, 2018 12:29 am

Re: Calculating Sig Figs

For all addition, subtraction, multiplication, and division, the number of decimal places in the result should be the same as the smallest number of decimal places in the data/question. When rounding, if the last digit of the number is >5, round up. If the last digit is <5, round down, and if the last digit ends in 5, round to the nearest even number.

Phoebe Chen 4I
Posts: 55
Joined: Fri Sep 28, 2018 12:29 am

Re: Calculating Sig Figs

For adding and subtracting, you just do the calculation in the normal fashion. After you get a number, your answer is only allowed to have as many decimal places as one of the numbers you started with with the least amount of decimal places. For example if you did 5.678 + 3.4 = 9.078. 3.4 is one of the numbers you started with and it has the least amount of decimal places, being only 1. That means your answer can only have one decimal places. In this case you would round up because the number after 0 is great than 5. So your answer will be 9.1. If the number after 0 was less than five, you would round down to 9.0.
For multiplication and division, you do the normal calculation then your final answer form is only allowed to have as many sig figs as the number you started with that has the least amount of sig figs. For example: 87,000*2.848 = 247,776. 87,000 has the least amount of sig figs being two, so your answer will be 250,000. And we rounded up because the number after 4 was greater than 5.

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