1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Stats: finding probability in normal distribution

  1. Jun 2, 2008 #1
    1. The problem statement, all variables and given/known data

    Find Z0 such that P(z > z0) = 0.1234

    2. Relevant equations

    3. The attempt at a solution

    Z is the mean which is 0. So if Z0 is less than the mean it should be a negative number. Looking at the table 0.1234 does not show up but the closest is 0.1217 which is 0.31.
    So Z0 is -0.31?
  2. jcsd
  3. Jun 2, 2008 #2
    It depends on if you're saying from [itex]-\infty \leq z \leq z0[/itex] or [itex]0 \leq z \leq z0[/itex]. The value you found is for the latter (+0.31). It sounds like intuitively you are thinking of the former case, but used the table for the latter case.

    Here if you needed another table-- http://www.math.unb.ca/~knight/utility/NormTble.htm [Broken]
    Last edited by a moderator: May 3, 2017
  4. Jun 2, 2008 #3


    User Avatar

    Z is not the mean, it is the standard normal random variable. You want to find P(Z > z0). So you want to find P(Z<z0) such that it equals to 1-P(Z>z0). 1-0.1234=0.8766, which corresponds to about z0=1.155 from the table David posted
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook