document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=871483>Question 871483</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I need help with this question, thank you in advance!!! \r<BR>\n" );
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document.write( "A study has shown that 20% of all college textbooks cost at least $70. It is known that the standard deviation of the prices of the college textbook is $9.50. Assuming that prices of all college textbooks follows a normal distribution; find the mean price of all college textbooks.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #525630 by </B><A HREF=/tutors/aboutme.mpl?userid=rothauserc><B>rothauserc(4718)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rothauserc><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=rothauserc><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=525630\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> We are given Pr(X<70) = 0.20 or 20%<BR>\n" );
document.write( "consult z tables for z value associated with 0.20<BR>\n" );
document.write( "z value is -0.84<BR>\n" );
document.write( "we know that the z value is  (X - mean of x) / standard deviation<BR>\n" );
document.write( "therefore<BR>\n" );
document.write( "-0.84 = (70 - mean) / 9.50<BR>\n" );
document.write( "70 - mean = -0.84 * 9.50 = -7.98<BR>\n" );
document.write( "-mean = -7.98 -70<BR>\n" );
document.write( "mean = $77.98\r<BR>\n" );
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