Posted by Anonymous on .
a study shown that 20% of all college textbooks cost at least $70.it is known that the standard deviation of the prices of all college textbook is $9.50.assuming that prices of all college textbooks follow a normal distribution, find the mean price of all college textbooks.

final exam 
bobpursley,
http://www.jiskha.com/display.cgi?id=1369182329
Put in this applet the standard deviation, then the mean as zero.
Then start at 6, check the area. EVentually, you will get an area of .20
Then, say 6.5 is the point, you know that is really 70, so add 70 +6.5, and you have the mean.