1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How to find standard deviation

  1. Aug 3, 2017 #1
    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.
  2. jcsd
  3. Aug 3, 2017 #2


    User Avatar
    Science Advisor

    What is the definition of the standard deviation?
  4. Aug 3, 2017 #3


    User Avatar
    Homework Helper

    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.
  5. Aug 7, 2017 #4

    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.

  6. Aug 9, 2017 #5


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    Yes you were. WBahn gave you link http://bfy.tw/DBqv
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted