How to find standard deviation

1. Aug 3, 2017

zak100

1. The problem statement, all variables and given/known data

For the five data 0, 7, 8, 10, and 10 find the standard deviation.

2. Relevant equations

I know the formula:
Z = (X-Mew)/Sigma
Sigma = Standard Deviation
Mew = Mean = 7
X= score?
Z= number of standard deviation=?

3. The attempt at a solution
I have found mean which is 7 but i dont know how to find Z & X. Some body please guide me.
Zulfi.

2. Aug 3, 2017

mjc123

What is the definition of the standard deviation?

3. Aug 3, 2017

RUber

You are not being asked for Z, and all your X values are given. What you are missing is the sigma, or standard deviation.
In case your google search for "how to calculate standard deviation" didn't return any results, here is a start.
Standard deviation is defined as the square root of the variance, which is the average of the squared distances from the mean.
In formulaic terms, you have:
$\sigma^2 = \frac{ \sum_{i = 1}^N (X_i-\mu)^2 }{N}$
If these data refer to a sample and not the whole data set, then your denominator changes to (N-1). That's all.

4. Aug 7, 2017

zak100

Hi,
Hi,

I was not aware of the formula provided in post#3. I thought there is only one formula. Through post#3 I am able to find out the difference between the two formulae. To use the one provided in post#3, all X values must be provided:

Sigma^2 = ((0-7)^2 + (7-7)^2 + (8-7)^2 + (10-7)^2+ (10-7)^2)/5 = 68/5

Therefore sigma= 3.7

Thanks, God bless you.

Zulfi.

5. Aug 9, 2017

BvU

Yes you were. WBahn gave you link http://bfy.tw/DBqv