# Stats: finding probability in normal distribution

1. Jun 2, 2008

### yellowduck

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. Jun 2, 2008

### DavidWhitbeck

It depends on if you're saying from $-\infty \leq z \leq z0$ or $0 \leq z \leq z0$. 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
3. Jun 2, 2008

### exk

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