Homework Help: Pre-calculus

Posted by Mary on Friday, January 16, 2009 at 4:21am.

A set of data is normally distributed with a mean of 500 and standard deviation of 40.

a). What percent of the data is between 460 and 540?
P(460<x<540)=P(-1<z<1)
=0.8413-0.1587
=0.6826
b). Find the probabilty that a value selected at random is less than 420.
P(x<420)=P(z<(420-500)/40)
=P(z<-2)
=0.0228
are these right?

Pre-calculus - Reiny, Friday, January 16, 2009 at 8:29am
both correct.

You might find this applet very useful.

http://davidmlane.com/hyperstat/z_table.html

It eliminates the use of charts and tables, you you don't even have to convert to z-scores

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