document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1147388>Question 1147388</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The ages of commercial aircraft are normally distributed with a mean of 13 years and a standard deviation of 7.7672 years . what percentage of individual aircraft have ages between nine years and 16 years ? assume that a random sample of 64 aircraft is selected and the mean age of the sample is computed what percentage of sample means had ages between nine years and 16 years? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #768709 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=768709\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> this is a z test<BR>\n" );
document.write( "for first part, z=(x-mean)/sd, and that is between -4/7.7672 or -0.51 and z=3/7.7672 or +0.39.  That probability is 0.3467\r<BR>\n" );
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document.write( "z=(x bar- mean)/sd/sqrt(n)<BR>\n" );
document.write( "lower z is > (9-13)*8/7.7672, moving sqrt (64)=8 to numerator.<BR>\n" );
document.write( "That is z >-4.12<BR>\n" );
document.write( "upper z is 3*8/7.7672<BR>\n" );
document.write( "that is z>3.09<BR>\n" );
document.write( "that probability with those z constraints is 0.9990. </SPAN>\n" );
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