Precalculus
posted by Mary .
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)
=0.84130.1587
=0.6826
b). Find the probabilty that a value selected at random is less than 420.
P(x<420)=P(z<(420500)/40)
=P(z<2)
=0.0228
are these right?

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 zscores
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