General sig figs question

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Aliya Jain 2B
Posts: 80
Joined: Wed Sep 11, 2019 12:16 am

General sig figs question

Postby Aliya Jain 2B » Thu Oct 03, 2019 12:47 pm

Does anyone know the rules for sig figs when adding or subtracting? I know that it differs from multiplying/dividing, but I don't remember how.

Camellia Liu 1J
Posts: 51
Joined: Sat Aug 24, 2019 12:15 am

Re: General sig figs question

Postby Camellia Liu 1J » Thu Oct 03, 2019 12:51 pm

I'm pretty sure that you start by counting the number of sig figs in the decimal part of the number in the problem. You add or subtract normally and then you round the answer to the least number of places in the decimal part of your final answer.

For multiplying/dividing, the least number of sig figs in the given numbers within the problem determines the final number of sig figs in your answer.

cassidysong 1K
Posts: 80
Joined: Fri Aug 30, 2019 12:15 am

Re: General sig figs question

Postby cassidysong 1K » Thu Oct 03, 2019 12:58 pm

I'm pretty sure significant figures when adding or subtracting are dictated by the lowest amount of numbers after the decimal.
Ex. 12.5+5.35=17.9

Alice Chang 2H
Posts: 80
Joined: Fri Aug 30, 2019 12:18 am

Re: General sig figs question

Postby Alice Chang 2H » Thu Oct 03, 2019 2:39 pm

This is something I found while looking up rules for sig figs, hope this helps:

For addition and subtraction use the following rules:

1. Count the number of significant figures in the decimal portion ONLY of each number in the problem
2. Add or subtract in the normal fashion
3. Your final answer may have no more significant figures to the right of the decimal than the LEAST number of significant figures in any number in the problem.

For multiplication and division use the following rule:

1. The LEAST number of significant figures in any number of the problem determines the number of significant figures in the answer. (You are now looking at the entire number, not just the decimal portion)
*This means you have to be able to recognize significant figures in order to use this rule*

Example: 5.26 has 3 significant figures

6.1 has 2 significant figures

AGulati_4A
Posts: 74
Joined: Sat Sep 07, 2019 12:19 am

Re: General sig figs question

Postby AGulati_4A » Thu Oct 03, 2019 2:43 pm

When adding or subtracting, you always take the number with the lowest # of sig figs; this is so that you are not making the answer more precise than any of its individual parts. Watch this Khan Academy video, it's so helpful: https://www.khanacademy.org/math/arithm ... nt-figures

Joelle 3L
Posts: 50
Joined: Sat Jul 20, 2019 12:16 am

Re: General sig figs question

Postby Joelle 3L » Thu Oct 03, 2019 3:22 pm

When determining the amount of sig figs for adding and subtracting you would just round the least amount of decimal places. For example 45.777+23.1=68.9. However for multiplying and subtracting, the rules are different. The least amount of sig figs in the number would determine how you would round. For example, 3.4*5.67=19 since the least amount if sig figs is 2.


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