# Homework Help: 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