document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=133640>Question 133640</A>This question is from textbook <A HREF=http://www.amazon.com/exec/obidos/ASIN/9780073534961/algebrahomeworkh>Statistics</A><BR>\n" );
document.write( ": <I><SPAN STYLE=\"word-break: break-all;\"> The average age of Amtrak passenger train cars is 19.4 years.  If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #98718 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=98718\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation.<BR>\n" );
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document.write( "mu = 19.4<BR>\n" );
document.write( "Find the z-value associated with upper 20%: <BR>\n" );
document.write( "InvNorm(0.80) = 0.8416<BR>\n" );
document.write( "Use z = (x-mu)/sigma to find sigma<BR>\n" );
document.write( "0.8416 = (22.8-19.4)/sigma<BR>\n" );
document.write( "sigma = (22.8-19.4)/0.8416<BR>\n" );
document.write( "sigma = (3.4)/0.8416 = 4.0399<BR>\n" );
document.write( "==================================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. <BR>\n" );
document.write( " </SPAN>\n" );
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