The .15% is the tail end of the probability distribution.
Probability distributions are such that the total area is 1.0 from Z=-∞ to Z=+∞.
For the normal distribution, Z=0 is at 0.5, which means that the probability of a variable falling above 0 is exactly that of falling below 0.
Here you're looking for the value of Z for which the probability of a variable falling above Z is 0.15, and below is 0.85. So look up the table (below) for Z such that the entries of the table is 0.85, which corresponds to a Z=1.04.
Also, check the little sketch in the following table:
http://www.math.unb.ca/~knight/utility/NormTble.htm
Having problems reading the z-table. I don't understand how .1500% equates to a 1.04 z-score
Thank you for your help
1 answer