Posted by jason on Wednesday, December 9, 2009 at 8:57pm.
For a standard normal curve, find the zscore that separates the bottom 90% from the top 10%.

MathStatistics  PsyDAG, Thursday, December 10, 2009 at 10:34am
In the back of your statistics text, there is a table labeled something like "areas under the normal distribution." Look for the portion values for the larger or smaller portion to get your Z score.
I hope this helps.