document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1173270>Question 1173270</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Oil Changes A service station advertises that<BR>\n" );
document.write( "customers will have to wait no more than 30 minutes for<BR>\n" );
document.write( "an oil change. A sample of 28 oil changes has a standard<BR>\n" );
document.write( "deviation of 5.2 minutes. Find the 95% confidence<BR>\n" );
document.write( "interval of the population standard deviation of the time<BR>\n" );
document.write( "spent waiting for an oil change. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #798503 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=798503\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> This is a Chi Square with df=27<BR>\n" );
document.write( "(n-1) s^2/ChiSq 0.025, df=27 < sigma ^2 < (n-1)s^2/ChiSq 0.975,df=27<BR>\n" );
document.write( "26*27.04/43.195 < 26*27.04/14.573 Chi Square from the table<BR>\n" );
document.write( "=16.28 < sigma ^2 < 48.24<BR>\n" );
document.write( "That is the 95% CI of the variance<BR>\n" );
document.write( "take the square root for the CI of the sd<BR>\n" );
document.write( "4.03 < sigma < 6.95<BR>\n" );
document.write( "or (4.03, 6.95) units minutes </SPAN>\n" );
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