document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1191081>Question 1191081</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A researcher is interested in finding a 95% confidence interval for the mean number minutes students are concentrating on their professor during a one hour statistics lecture. The study included 121 students who averaged 37.2 minutes concentrating on their professor during the hour lecture. The standard deviation was 13.3 minutes. Round answers to 3 decimal places where possible.\r<BR>\n" );
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document.write( "a. To compute the confidence interval use a <BR>\n" );
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document.write( "b. With 95% confidence the population mean minutes of concentration is between <BR>\n" );
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document.write( " minutes.\r<BR>\n" );
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document.write( "c. If many groups of 121 randomly selected members are studied, then a different confidence interval would be produced from each group. About <BR>\n" );
document.write( " percent of these confidence intervals will contain the true population mean minutes of concentration and about <BR>\n" );
document.write( " percent will not contain the true population mean minutes of concentration. \r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #822853 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=822853\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> I would use a t-distribution because the sd used is from the sample. Some might use a z- because the number is large. There won't be a big difference but t is more accurate<BR>\n" );
document.write( "half-interval is t(0.995,df=120)*ss/sqrt(n)=2.617*13.3/11<BR>\n" );
document.write( "=3.164 min<BR>\n" );
document.write( "the interval is (34.036, 40.364)units min.<BR>\n" );
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document.write( "95% for first part<BR>\n" );
document.write( "5% for second part\r<BR>\n" );
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