Results 1 to 6 of 6

Math Help - standard deviation

  1. #1
    Junior Member
    Joined
    Apr 2009
    Posts
    44

    standard deviation

    data was collected outside a popular new restaruant to determine the ean waiting time to be seated at a table

    mean,45 min
    standard deviation,12 min

    determine the probability that a person has to wait less than twenty minutes.

    also,determine the probability a person has to wait more than an hour.

    do I have to calculate the z scores then look on the table,I've always hated standard deviation stuff I never get it
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    29
    Z= \frac{X-\mu}{\sigma}

    P(X<20) = P\left(Z<\frac{20-25}{12}\right) = P(Z<-0.42)

    P(X>60) = P\left(Z>\frac{60-25}{12}\right) = P(Z>2.92)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    mean,45 min....not 25
    And I guess the underlying distribution is normal, otherwise I have no idea how to proceed.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    29
    Quote Originally Posted by matheagle View Post
    mean,45 min....not 25
    Z= \frac{X-\mu}{\sigma}

    P(X<20) = P\left(Z<\frac{20-45}{12}\right) = P(Z<-2.08)

    P(X>60) = P\left(Z>\frac{60-45}{12}\right) = P(Z>1.25)

    Quote Originally Posted by matheagle View Post
    And I guess the underlying distribution is normal, otherwise I have no idea how to proceed.
    most importantly! The mention of z-scores was the only hint.
    Last edited by pickslides; May 31st 2009 at 03:09 PM. Reason: typo
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by pickslides View Post
    Z= \frac{X-\mu}{\sigma}

    P(X<20) = P\left(Z<\frac{20-45}{12}\right) = P(Z<-2.08)

    P(X>60) = P\left(Z>\frac{60-45}{12}\right) = P(Z>1.25)



    most importantly! The mention of z-scores was the only hint.
    z-scores were mentioned by the student (almost as a hopeful stab in the dark), not in the question itself. So it's not quite in the league of a hint.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Master Of Puppets
    pickslides's Avatar
    Joined
    Sep 2008
    From
    Melbourne
    Posts
    5,236
    Thanks
    29
    Quote Originally Posted by mr fantastic View Post
    z-scores were mentioned by the student (almost as a hopeful stab in the dark), not in the question itself. So it's not quite in the league of a hint.
    fair call.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Standard Deviation
    Posted in the Statistics Forum
    Replies: 4
    Last Post: September 8th 2010, 04:05 AM
  2. Replies: 5
    Last Post: May 18th 2009, 05:14 AM
  3. standard deviation and mean deviation
    Posted in the Statistics Forum
    Replies: 1
    Last Post: March 16th 2008, 06:09 AM
  4. i need standard deviation help
    Posted in the Statistics Forum
    Replies: 2
    Last Post: February 22nd 2008, 06:03 PM
  5. The mean and standard deviation
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: February 17th 2008, 09:15 PM

Search Tags


/mathhelpforum @mathhelpforum