# Math Help - Standard Deviation and Varians

1. ## Standard Deviation and Varians

I first of all apologize if this is the wrong category. This is for a Statics class at college level, but basic statistics.

I am really having a hard time and confusing myself when it comes to the standard deviation and variations. The formulas (do the best I can without the keys needed on the keyboard) are:

O2m = O2 squared / N - this is variance

Om = this is standard deviation (standard deviation / N squared = standard deviation)

When given a problem are we be given one or the other to calcuate and then continue with the rest of the steps. For example if I am given the standard deviation of 8 and my N = 10 then 8/10 = .80 so this would be my standard deviation.

Would I also then calcuate a variance or or is that only if you are given the variance in the problem you would then use the formula to determine your variance.

This is the only part I am having a really hard time grasping. Ugh.

Thanks for your help!!

2. Hello Nurse Toby.

The problem seems to be the terminology
Let $\sigma^2$ be the variance of one observation whether thats $X_1$ or $X_2$....
It's the variance of each one of them.

NOW the sample mean is $\bar X={X_1+...+X_n\over n}$

and the variance of $\bar X$ is $\sigma^2/n$

and the st deviation of $\bar X$ is $\sigma/\sqrt{n}$

3. Originally Posted by nursetobe
This is for a Statics class at college level
Statics??? I thought you wanted to be a nurse, not an engineer.

Originally Posted by matheagle
Hello Nurse Toby.
hahahaha

4. Thanks for your help matheagle

Anonymously, trust me if it were up to me I wouldn't be taking statistics but it is required for a BSN!!

Great site by the way!!!

5. You're welcome, my friends call me the beagle, short for mathbeagle my alter ego
I solve math problems during the day and fight crime at night
no wait, it's the other way around