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Thread: Statistics Marathon & Questions

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    Statistics Marathon & Questions

    Statistics Marathon & Questions
    This is a marathon thread for statistics. Please aim to pitch your questions for first-year/second-year university level statistics. Excelling & gifted/talented secondary school students are also invited to contribute.

    This is also a place to discuss university level statistics. For specific subjects or even higher level stuff, this is probably not the best thread. (Feel to create your own in those instances)

    (mod edit 7/6/17 by dan964)

    ===============================













    Last edited by dan964; 14 Jun 2017 at 1:25 PM.
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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by davidgoes4wce View Post
    Thought it'd be a good idea to start a marathon for users to post and answer university statistics and probability problems.











    Remember that variance is the square of standard deviation.

    They gave us the standard deviations of the male and female masses, so we need to square them to get their variances to use in your line about variance.

    Then to get the standard deviation at the end, we'll need to take the square root of what you get for the variance.
    Last edited by InteGrand; 3 May 2016 at 10:38 AM. Reason: Typo

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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by InteGrand View Post
    Remember that variance is the square of standard deviation.

    They gave us the standard deviations of the male and female masses, so we need to square them to get their variances to use in your line about variance.

    Then to get the standard deviation at the end, we'll need to take the square root of what you get for the variance.
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    Re: University Statistics Discussion Marathon

    Where are you getting 4X and 3Y from? You are not multiplying single R.V's by a constant, you are summing independent identically distributed R.V's.

    (These things aren't actually independent, but this is a good approximation if the number of people in the office is much larger that the number of people in the lift for example.)

    When you sum independent (more generally uncorrelated) R.V's, you just sum the variances of the individual R.V's to obtain the variance of the sum. This gives you the correct answer.

    (Apologies for anything said above that is incorrect, my stats knowledge is mediocre).

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    Re: University Statistics Discussion Marathon

    Re: my comment on independence.

    We can see the extreme case of how this method breaks down if there are exactly 4 men and 3 women in the whole office. Then there is only one way to choose the occupants of the elevator, and so the total mass will have zero variance, regardless of how widely the masses of the individual people vary.

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    Re: University Statistics Discussion Marathon

    I still don't get their answer.....im thinking it should be 53.67







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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by davidgoes4wce View Post
    I still don't get their answer.....im thinking it should be 53.67







    As I just said, 4X and 3Y are irrelevant to the problem. We have

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    Re: University Statistics Discussion Marathon

    Think about rolling a dice and doubling the outcome vs rolling two dice and summing them.

    The first RV only takes even values and takes each value in {2,4,...10,12} with equal likelihood.
    The second RV can take any value in {2,3,...,11,12} and takes the values close to 7 much more often than it takes the values far from 7.

    We have an analogous situation in your elevator question and you are mixing up the above two.
    Last edited by seanieg89; 3 May 2016 at 1:28 PM.

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    Re: University Statistics Discussion Marathon

    I'm starting probability next lecture. Should I post all of my questions here?

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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by leehuan View Post
    I'm starting probability next lecture. Should I post all of my questions here?
    I guess that's up to you. If you'd prefer having your own questions in specific threads, you could make separate threads for them. Depends on whether you'd prefer that or prefer having them in one thread that also includes Q's from other people.

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    Re: University Statistics Discussion Marathon

    Here is a exercise that some of you might enjoy from a probability course I am grading:


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    Re: University Statistics Discussion Marathon

    One of the few questions I got out by myself. (Good revision for you I suppose david)




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    Re: University Statistics Discussion Marathon

    Does anyone in here have access to the solutions manual for Business Statistics by Selvanathan, E., Selvanathan, S. and Keller, G? If there are any students that studied that course before that still have the weekly tutorials from their respective universities or tutors or lecturers that have access to the solutions (as I am trying to do as many questions as possible to get my standards up). If there is a price and terms you have for them, please message me.
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    Re: University Statistics Discussion Marathon

    Probably an easy question compared to the questions you guys post but I need help with this.

    For the class of 2010, the average score on the Writing portion of the SAT (Scholastic Aptitude Test) is 492 with a standard deviation of 111. Find the mean and standard deviation of the distribution of mean scores if we take random samples of 1100 scores at a time and compute the sample means.

    Round your answer for the mean to the nearest integer, and your answer for the standard deviation to two decimal places.

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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by BlueGas View Post
    Probably an easy question compared to the questions you guys post but I need help with this.

    For the class of 2010, the average score on the Writing portion of the SAT (Scholastic Aptitude Test) is 492 with a standard deviation of 111. Find the mean and standard deviation of the distribution of mean scores if we take random samples of 1100 scores at a time and compute the sample means.

    Round your answer for the mean to the nearest integer, and your answer for the standard deviation to two decimal places.
    Bump.

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    Re: University Statistics Discussion Marathon

    Not sure if you have a solution with you but I think the mean would still be the same = 492, the standard deviation would it be 3.35 (to 2 decimal places)?
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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by davidgoes4wce View Post
    Not sure if you have a solution with you but I think the mean would still be the same = 492, the standard deviation would it be 3.35 (to 2 decimal places)?
    How did you get that solution?

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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by BlueGas View Post
    How did you get that solution?
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    Re: University Statistics Discussion Marathon

    I attempted this next question and wanted to make sure if I'm right.

    Test whether males are less likely than females to support a ballot initiative, if 24 % of a random sample of 52 males plan to vote yes on the initiative and 31 % of a random sample of 52 females plan to vote yes.

    P1 is for males who said yes and P2 is for females who said yes

    P1 = 0.24
    P2 = 0.31
    Pooled proportion = 0.275

    Test Statistic = -0.80
    P-value = 0.212

    and the conclusion is do not reject the null hypothesis as the p-value as greater than the significance level of 5%

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    Re: University Statistics Discussion Marathon




















    Last edited by davidgoes4wce; 23 May 2016 at 11:29 PM.
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    Re: University Statistics Discussion Marathon

    Nice, thanks mate!!

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    Re: University Statistics Discussion Marathon

    Need help with this


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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by BlueGas View Post
    Need help with this

    Bump.

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    Re: University Statistics Discussion Marathon















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    Re: University Statistics Discussion Marathon

    Quote Originally Posted by davidgoes4wce View Post














    Thanks for the method, much appreciated!

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