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Math Help - Need quick help for intermediate computation

  1. #1
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    Need quick help for intermediate computation

    A newspaper article reported that people spend a mean of hours per day watching TV, with a standard deviation of hours. A psychologist would like to conduct interviews with the of the population who spend the most time watching TV. She assumes that the daily time people spend watching TV is normally distributed. At least how many hours of daily TV watching are necessary for a person to be eligible for the interview? Carry your intermediate computations to at least four decimal places. Round your answer to at least one decimal place.







    i'm absoultley horrible with this and i am a bit confused as far as the hours go... i would appreciate any help thanks
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  2. #2
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    Let Y be the number of hours watched, so Y~N(6.5,1.8^2)
    You want to find some y such that
     <br />
P(Y>y)=0.2<br />

    So by standardising,
    P\left(\frac{Y-\mu}{\sigma}>\frac{y-\mu}{\sigma}\right)
    P(Z>\frac{y-6.5}{1.8})=.2
    so from a standard normal table (or use a calculator Z table - Normal Distribution), you can see that z=\frac{y-6.5}{1.8}=.8416
    so you need to solve for y to find the number of hours.
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  3. #3
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    so that would pur y = 8.01488 or just 8 in this equation as the answer???
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