Results 1 to 5 of 5

Math Help - Normal Distribution/Z-table usage

  1. #1
    Newbie
    Joined
    Jun 2008
    Posts
    11

    Unhappy Normal Distribution/Z-table usage

    Hi there!

    I've been really perplexed by this for the past hour or so, so I'd really appreciate it if you could help me.

    So I have this:

    0.5 - P(0 < Z < 0.6667)
    = 0.5 - 0.2475
    = 0.2525

    I don't understand how P(0<Z<0.6667) was solved. How do I find 0.6667 in the Z-table, as it only goes to two decimal places? I've been stumped every time I come across a number with three or more decimal places.

    Thank you in advance!

    NB. The Z-table that has been provided to us only goes up to 0.9 at the top and 3.0 down the side, hence my confusion.
    Last edited by trackies; June 9th 2008 at 01:40 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Feb 2008
    From
    Berkeley, Illinois
    Posts
    364
    Quote Originally Posted by mr fantastic View Post
    I have no time now but will reply later if no-one else does.
    For the mathematical answer to your question, go here:

    Probability of a Random Variable in the Normal Distribution

    Press the appropriate probability button, in this case, the third one, and Enter 0 and .667 and press the Calculate button. It will show you the math.

    Now, for an in depth description. The normal distribution follows a bell curve, the theory being, that 1/2 of all possible cases rests at 0, based on a Z score which is (X - mu)/sigma.

    With respect to your table, everybody works differently. I have a book that uses 2 decimal places. For you, I'd round and look for 0.67. If you want to split hairs, you can interpolate between 0.66 and 0.67 if you are familiar with interpolation.

    Or, use Excel for exact decimals: =NORMSDIST(0.667)-NORMSDIST(0)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Hello,

    Quote Originally Posted by mathceleb View Post
    For the mathematical answer to your question, go here:

    Probability of a Random Variable in the Normal Distribution

    Press the appropriate probability button, in this case, the third one, and Enter 0 and .667 and press the Calculate button. It will show you the math.

    Now, for an in depth description. The normal distribution follows a bell curve, the theory being, that 1/2 of all possible cases rests at 0, based on a Z score which is (X - mu)/sigma.

    With respect to your table, everybody works differently. I have a book that uses 2 decimal places. For you, I'd round and look for 0.67. If you want to split hairs, you can interpolate between 0.66 and 0.67 if you are familiar with interpolation.

    Or, use Excel for exact decimals: =NORMSDIST(0.667)-NORMSDIST(0)
    If you read a table normally, you can see that P(0<Z<x)=0.2475 \not \implies x=0.67, which means that it hasn't been rounded.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Jun 2008
    Posts
    11
    Thank-you so much for your replies! My friend was online briefly and explained interpolation to me, so I managed to use that.
    Last edited by trackies; June 9th 2008 at 10:49 PM. Reason: typo
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by trackies View Post
    NB. The Z-table that has been provided to us only goes up to 0.9 at the top and 3.0 down the side, hence my confusion.
    If you re-examine your table you will find it goes to 3.0 in steps of 0.1 downwards, and from 0.00 to 0.09 in steps of 0.01 accross.

    To look up z=0.6667 look up z=0.66 and z=0.67, the value you seek is 2/3 of the way between the tabulated values just looked up.

    RonL
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Normal distribution table values
    Posted in the Statistics Forum
    Replies: 4
    Last Post: May 22nd 2011, 11:06 PM
  2. Normal Distribution table
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: May 6th 2010, 11:22 PM
  3. Distribution Table
    Posted in the LaTeX Help Forum
    Replies: 6
    Last Post: July 30th 2009, 03:16 PM
  4. Replies: 5
    Last Post: July 26th 2008, 02:53 PM
  5. Interpolating Normal Distribution Table
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: May 2nd 2008, 05:20 AM

Search Tags


/mathhelpforum @mathhelpforum