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### Significant Figures

Posted: **Tue Oct 02, 2018 3:10 pm**

by **katherinemurk 2B**

Can someone explain addition and subtraction with significant figures? We went over it in discussion today but I was still confused about how many significant figures should be in the final answer?

### Re: Significant Figures

Posted: **Tue Oct 02, 2018 3:17 pm**

by **Jessica Chen 1F**

The answer should have as many sigfigs as the LEAST # of sigfigs in the given problem.

For example, if you were told to subtract 1.702 (4 sigfigs) from 5.0 (2 sigfigs), your answer should only have 2 sigfigs and is 3.3.

### Re: Significant Figures

Posted: **Tue Oct 02, 2018 5:32 pm**

by **Tam To 1B**

When you do sig figs for addition/subtraction, only think about the amount of digits after the decimal point.

First you would do addition/subtraction normally, then afterwards you would round your answer to the least number of places in the decimal portion of the numbers you added/subtracted.

For example:

1.032 + 122.5 + 10.64 = 134.172

Since 122.5 has the smallest amount of figures after the decimal point, 1, the answer would be rounded to 134.2.

Hope this helps!

### Re: Significant Figures

Posted: **Tue Oct 02, 2018 6:02 pm**

by **Katie Frei 1L**

Does anyone know why you would round to the nearest even number if the number ends in 5? For example if 2.85 was to have two significant figures, why would I write 2.8 instead of round up to 2.9? Thanks!

### Re: Significant Figures

Posted: **Tue Oct 02, 2018 10:03 pm**

by **taryn_baldus2E**

Does anybody know if you must maintain a correct number of significant figures while working out, for example, a molarity problem, or if you would simply apply the correct number of significant figures once you have found your solution?

### Re: Significant Figures

Posted: **Tue Oct 02, 2018 10:52 pm**

by **Ian Marquez 2K**

taryn_baldus3A wrote:Does anybody know if you must maintain a correct number of significant figures while working out, for example, a molarity problem, or if you would simply apply the correct number of significant figures once you have found your solution?

When working through a problem, I believe that rounding to maintain a correct number of significant figures should be applied after all the calculations have been done. This prevents possible rounding errors that could be encountered if the numbers are rounded off after each subsequent step with either dividing or multiplying. Once you find your solution, then the insignificant figures can be dropped.

### Re: Significant Figures

Posted: **Wed Oct 03, 2018 7:41 pm**

by **Nicklas_Wright_1A**

You must keep track of significant figures throughout your calculations, however you should not round until the end. If you need to, you can write down how many significant figures each number has as you go through each step, just remember to keep the numbers unrounded. Pay particular attention to logarithms, exponentials, addition, and subtraction because these can cause changes in the number of significant figures.