Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter

    I am told to find the standard deviation of this data x 11 13 15 20 25

    I know that standard deviation is the square rooting of the variance but how would you go about this bearing in mind in includes x's?

    what was the standard diviation ? and what exactly are you trying to find out x or the varience?

    you may have to find the standard deviation in terms of x? Unless there's any other information given so that you can actually work out x using that?

    Sum them all up, you should get something like:

    A + x

    Where A is a real number.

    Then divide that number by the total of numbers of values you have, in your case it is 6 giving you something like this giving you the mean..

    \mu = \dfrac{A}{6}+\dfrac{x}{6}

    Then for each value from your set of values, subtract the mean and square the value you get. For these set of values, we will call them squared values.

     x_1=x, x_2=11, x_3=13 \cdots


                          (x_1-\mu)^2 = (x - (\dfrac{A}{6}+\dfrac{x}{6}))^2

                          (x_2-\mu)^2 = \cdots


    Add the squared values all up and then work out the mean of the squared values by dividing by 6... This is your variance...

      \sigma^2 = \dfrac{1}{6}((x_1-\mu)^2+(x_2-\mu)^2+(x_3-\mu)^2 +\cdots)

    Then square root that value and you have you standard deviation, you should end up with an algebraic equation.

    I've just been looking at this


    It tells me that you can come up with a good estimate for sd by range divided by 4.

    An estimate then would be (25-x)/4

    Is that any use to you?
    • Thread Starter

    Posted from TSR Mobile

    Thanks I worked in the end you don't use include the x.
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
    Useful resources

    Make your revision easier


    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here


    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.