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Math Help - Norm Dist (excel)

  1. #1
    Sep 2008

    Norm Dist (excel)

    Let X ~Normal(200, 60). Use Excel (Use the functions NORMDIST or NORMSINV, and fill in the dialogue box appropriately) to find the following.

    k such that P(X>k)=0.01?

    This is the only one giving me problems I use the normdist formula in excel and i enter the mean std deviation and the value (True/False) but I don't see how I can solve for a specific value, unless i just keep doing trial and error and i know this is not the right way to go about it.

    thanks for any help.
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  2. #2
    MHF Contributor
    Aug 2007
    You must simply ponder the defintions of the functions until it soaks in.

    p(X>k) = 0.01 is the same as p(X<=k) = 0.99

    =NORMSINV(0.99) gives 2.326348
    Note: =NORMSINV(0.01) = -2.326348 and symmetry can be used to achieve the same result.

    I'll let you fill in the last blank.


    Figure out what the last "1" is, too.
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  3. #3
    Sep 2008
    I can't work out what goes there, but i get that the one is the same as writing true.

    But I am lost.

    I have another question and I think that I am supposed to use the same idea,

    A machine fills bottles of soft drink to a mean volume of 510 ml with a standard deviation of 10 ml. Assume the the volumes of the bottles are normally distributed. The label on the bottle specifies a volume of 500ml.

    What percentage of bottles is under-filled?

    I have found this to be 0.158655

    In order to reduce the percentage of under-filled bottles to 1%, the company decides to adjust the standard deviation of the volumes filled by the machine. What should the new standard deviation be?

    Am I right in thinking that I am supposed to use the same process as in the first question?
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