document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1041531>Question 1041531</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A study of 35 bolts of carpet showed that their average length was 70.2 yards. The standard deviation of the population is 1.6 yards. Which of the following is the 95% confidence interval for the mean length per bolt of carpet?<BR>\n" );
document.write( "A. 69.1 < &#956; < 71.3<BR>\n" );
document.write( "B. 69.9 < &#956; < 70.5<BR>\n" );
document.write( "C. 69.8 < &#956; < 70.6<BR>\n" );
document.write( "D. 69.7 <&#956; < 70.7<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #656488 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=656488\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The standard error is t(0.975, df=34)s/sqrt (n)<BR>\n" );
document.write( "=2.0322*1.6/sqrt(35)<BR>\n" );
document.write( "=0.5496, or 0.55<BR>\n" );
document.write( "(69.65,70.75), which I would round to (69.7,70.7)<BR>\n" );
document.write( "I would say D<BR>\n" );
document.write( "BUT, I am bothered by the sd of the population and not the sample. I think what the question wants you to do is to use a z-test because the sample is larger than 30 AND you know the population sd.  I don't have evidence of normality, which is another assumption needed, but if I accept that, then I would use a z-test but fortunately getting the same answer.  <BR>\n" );
document.write( "This would make it a z-test where the SE is 1.96*1.6/sqrt(35)=0,53, slightly different from above. </SPAN>\n" );
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