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Math Help - Two stats problems

  1. #1
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    Two stats problems

    I have the key book but my answers aren't coming up the same so I know I am messing up somewhere. If you can help I'd be very thankful

    a)
    If the mean salary for high school teachers in the US is $29,835 and the standard deviation is $3000, find the probability that a teacher makes more than $35,000.

    So I first have to find the Z score, which would be = 35,000-29835 / 3000

    Z= 1.72166

    which = .4657 (around) after looking at a chart

    and to find the probability above 35,000, I had .5000 - .4657 = .0341

    b)
    Houses in a certain neighborhood sell for an averae price of $126,000 with a standard deviation of $3,000. Find the Range for the middle 85% of houses in the neighborhood

    Ack I found what I did wrong. I misread it as 95% and treated it as a confidence interval problem.
    To find the correct answer, would I treat it as a Z score problem?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by aargh27 View Post
    I have the key book but my answers aren't coming up the same so I know I am messing up somewhere. If you can help I'd be very thankful

    a)
    If the mean salary for high school teachers in the US is $29,835 and the standard deviation is $3000, find the probability that a teacher makes more than $35,000.

    So I first have to find the Z score, which would be = 35,000-29835 / 3000

    Z= 1.72166

    which = .4657 (around) after looking at a chart

    and to find the probability above 35,000, I had .5000 - .4657 = .0341
    I don't know what table you are using but mine gives:

    P(Z<=1.72) = 0.9573,

    so:

    P(Z>1.72) = 1-0.9573 = 0.0427

    Also this is all invalid without a statement to the effect that the distribution
    of salaries is normal, or that you are assuming it so.

    RonL
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  3. #3
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    My table isn't exact so I estimated... and no, there is no statement about the the sales being normal but I am pretty sure I am ment to assume it, yes.
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