# Sig figs ! Help

ok so this may sound really dumb but i need to refresh my memory on this so here is the question

6.941+63.996+35.45 = 106.387

how do i know how many sig figs to round too with this?

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jedishrfu
Mentor
Since the 35.45 is not written as 35.450 then you have to use it as the limiting significant figures hence your answer would be 106.39

Since the 35.45 is not written as 35.450 then you have to use it as the limiting significant figures hence your answer would be 106.39
so you always use the smallest one correct?

CAF123
Gold Member
so you always use the smallest one correct?
Consider this: Say you are doing an experiment and you know one parameter to a good degree of precision and another parameter to a lesser degree of precision. Now say we have some other parameter that is dependent on these two parameters. When you combine them (i.e by dividing, multiplying etc) this dependent parameter will be affected by this parameter which you knew to a lesser precision. Hence, yes, you should quote your final result to the lowest number of sig fig in your data.

Borek
Mentor
so you always use the smallest one correct?
This is not exactly true.

100.23 + 0.11 = 100.34

but

100.23*0.11 = 11

Rules for addition and subtraction are slightly different than for multiplication and division.

Don't worry too much about significant figures. There are much better ways of expressing precision of the result. Sigfigs are more of a rule of thumb.