Results 1 to 2 of 2

Math Help - Z - Values

  1. #1
    Newbie
    Joined
    Oct 2005
    Posts
    2

    Question Z - Values

    Please read the following question:
    A lightbulb has a normally distributed light ouput with a mean
    5000 end foot-candles and standard deviation of 50 end foot candles.
    Find a lower specification limit such that only 0.5% of the bulbs
    will not exceed this limit.


    In order to solve this question I used Z = Mean - LSL / Sigma

    Z = .05 or .69146
    M = 5000
    Sigma = 50

    .69146 = 5000 - LSL / 50
    LSL = 5000 - ( 50 x .69146 )
    LSL = 4965.43

    The next question I believe uses Z = USL - Mean / Sigma

    If x is normally distributed with mean u and standard deviation four,
    and given the probability that x is less, than 32 is 0.0228, find the
    value of u

    Your comments please,

    Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    hpe
    hpe is offline
    Member hpe's Avatar
    Joined
    Apr 2005
    Posts
    158
    [QUOTE=Captain SoamesIn order to solve this question I used Z = Mean - LSL / Sigma
    [/quote]
    So far it's OK.
    Z = .05 or .69146
    That doesn't seem right. You want z s.th. Prob(Z > z) = 0.5% = 0.005. That leads to z = 2.57. Use this value of z in your calculation
    M = 5000
    Sigma = 50

    .69146 = 5000 - LSL / 50
    LSL = 5000 - ( 50 x .69146 )
    LSL = 4965.43
    ... and you'll get the correct LSL.
    The next question I believe uses Z = USL - Mean / Sigma

    If x is normally distributed with mean u and standard deviation four,
    and given the probability that x is less, than 32 is 0.0228, find the
    value of u
    .0228 is the probability of being more than 2 standard deviations below the mean. So the mean minus 2 std dev equals 32. From that you can find the mean \mu.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Predicting maximum values from minimum values
    Posted in the Statistics Forum
    Replies: 0
    Last Post: October 4th 2011, 08:42 AM
  2. Replies: 1
    Last Post: June 1st 2011, 02:47 AM
  3. Single values vs set of values in an equation
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: August 21st 2010, 04:45 AM
  4. Replies: 2
    Last Post: January 28th 2010, 02:39 AM
  5. Replies: 1
    Last Post: May 24th 2009, 06:16 AM

Search Tags


/mathhelpforum @mathhelpforum