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Math Help - normal distribution and probability

  1. #1
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    normal distribution and probability

    Hi, reagrding this on a normal curve.....

    Having a bit of trouble, i have an example for which i have worked out that that proabilty for x bieng bigger than 0.84 ( with a mean of 1.8 and a SD of 0.44) to be 0.9854
    I take it this is right, but now it wants to know p(1.0<x<2.0), and im not sure how to approach this.

    Any ideas????????

    ( also i posted something about confidence intervals in the advanced section and meant to post that in here, any help on that would be great aswell ).
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  2. #2
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    Quote Originally Posted by bobchiba View Post
    Hi, reagrding this on a normal curve.....

    Having a bit of trouble, i have an example for which i have worked out that that proabilty for x bieng bigger than 0.84 ( with a mean of 1.8 and a SD of 0.44) to be 0.9854
    I take it this is right, but now it wants to know p(1.0<x<2.0), and im not sure how to approach this.
    You need to find the z-score.

    1.8-.44z=.84
    Thus,
    z=2.181

    Here

    The probability is .4975

    But you need to double that because that is only half of the normal curve to get.
    .995
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  3. #3
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    are you sure..... the table shows 2.181 is .4854 have you made a mistake or do i still not get it???
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    Quote Originally Posted by bobchiba View Post
    are you sure..... the table shows 2.181 is .4854 have you made a mistake or do i still not get it???
    Sorry, I have that table memorized and mentally went down the wrong colomun.
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  5. #5
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    hi again, I am trying to work through these problem slooking at you r advice and some notes i have and i just cant seem to get my head around it.
    this is the exact question word for word:
    The Environment Protection Agency has developed a testing programme to monitor vehicle emission levels of several pollutants. Data collected under a variety of conditions suggests that the Normal curve provides an adequate approximation for the distribution of the key variable of interest, the amount of oxides of nitrogen (g/mile) emitted by a vehicle. The mean emission has been found to be 1.8 g/mile, with a standard deviation of 0.44 g/mile.

    Calculate the following:


    (a)The probability that a randomly selected vehicle emits more than 0.84 g/mile.



    I can get up to -2.181 through z = (0.84 - 1.8)/0.44 and then i get confused
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