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Math Help - 2 statistics problems I need help with

  1. #1
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    2 statistics problems I need help with

    I was just hoping someone could explain how to find the answer and ultimately give me the answer to these 2 questions because if I can see how something is worked out then I can do it for any other problem... so here they are:

    Question #1:
    In Montana Megabuck Lottery, six numbers out of 1 to 36 must be picked (in order, with no repetitions allowed). How many different tickets would one have to buy in order to be certain to win? Given the fact that the jackpot usually varies between $5 million and $12 million, and a ticket costs only $1, why does not anyone do it?


    Question 2

    Class Size| 10 15 20 25 30 35 40
    __________________________________________________ __________
    P(class size)| 0.10 0.10 0.15 0.25 0.20 0.10 0.10

    Find expected value & standard deviation of class size.

    I GREATLY appreciate the help and the time taken to do this to whoever does this.
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  2. #2
    MHF Contributor matheagle's Avatar
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    2 is easier
    The E(X) is just the product of the x values and the corresponding probabilities, so
    E(X)=(10)(.1)+\cdots + (40)(.1)
    where you can factor out a 10 to make the algebra bit easier.
    In order to get your st deviation, you first obtain the variance of X.
    I do that via the short cut formula, which is
    V(X)=E(X^2)-(E(X))^2
    where
    E(X^2)=(10)^2(.1)+\cdots + (40)^2(.1).

    As for 1, well I have trouble believing you want order.
    It's just 36 choose 6 balls, i.e.
    {36\choose 6}={36!\over 30! 6!}
    but that's without order.
    If you want to count order it's
    (36)(35)(34)(33)(32)(31)={36!\over 30!}
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