How to calculate significant digits

[CaitiePhr33k]

like, major help I have no idea what to do when calculating significant digits and stuff like that


those who help I thank very much so

 

[Danger]

Welcome to PF, Caitie.
I'm not entirely sure that I understand the question. If you mean how to decide upon how many decimal places to include in your answer, that's up to the requirements of the situation. In any event, it can't exceed the minimum accuracy involved in the parts of the calculation. (At least, that's the way that I was taught.) If you use 3.14 for pi, for instance, your answer would have to be rounded to 2 decimal places no matter how many are in the rest of the equation.

 

[CaitiePhr33k]

the one question is 164.5 min. i have to round to the appropriate number of significant digits and convert to the state unit of seconds

 

[Doc Al]

The number of significant figures in the answer depends upon the number of significant figures in the data used to compute the answer.

 

[CaitiePhr33k]

The number of significant figures in the answer depends upon the number of significant figures in the data used to compute the answer.

you lost me and now my head hurts

 

[dst]

you lost me and now my head hurts

It depends on the number of significant figures you start off with. If the question tells you to use, say, g = 9.8, you would give your answer to 2 s.f.

 

[CaitiePhr33k]

oh ok i kinda get it now

 

[wysard]

When calculating significant digits, you round to the term with the least significant digits (nubers of zeros) A few examples might help.

1) 1.03 x 2.245 rounded to 2 digits = 2.31
2) 2 x 2.25 rounded to 0 zero digits = 2

 

[LURCH]

you lost me and now my head hurts

LOL! I know just how you feel.

One aspect of sig figs that hasn't been mentioned, yet; this statement...

If you use 3.14 for pi, for instance, your answer would have to be rounded to 2 decimal places no matter how many are in the rest of the equation.

...is essentialy accurate, but it kind of leaves out something. The real trick to dealing with sig figs is that, if you multiply 1000 times Pi, and you use "3.14" for Pi, then you no longer carry the calculation out to two decimal spaces. Your answer would be "3140", and not "3141.59", nor "3140.00". You see that, if you start with only two decimal spaces of accuracy, and multiply by a thousand, your margin for error also multiplies by a thousand. If this is something you're doing for school, that is probably the point they want you to learn.

 

[Danger]

Hi, Lurch. Yeah, that's what I meant by 'minimum accuracy', but I sure didn't express it very well. Thanks for clarifying.