document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1123006>Question 1123006</A>: <I><SPAN STYLE=\"word-break: break-all;\"> In a random sample of 25 people, the mean commute time to work was 33.8 minutes and the standard deviation was 7.2 minutes.  Assume the population is normally distributed and use a t-distribution to construct a 95% confidence interval for the population mean.  What is the margin or error? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #739215 by </B><A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><B>jim_thompson5910(35256)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><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=739215\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=\"black\" face=\"times\" size=\"3\">Use a T-table such as <a  rel=nofollow HREF=\"http://www.sjsu.edu/faculty/gerstman/StatPrimer/t-table.pdf\">this one</a> to look up the critical T value that corresponds to a 95% confidence interval. <BR>\n" );
document.write( "Since n = 25 is the sample size, this means the degrees of freedom (df) is <BR>\n" );
document.write( "df = n-1<BR>\n" );
document.write( "df = 25-1<BR>\n" );
document.write( "df = 24<BR>\n" );
document.write( "Use a highlighter to mark the entire row that has df = 24.<BR>\n" );
document.write( "Mark the column that is over top the 95% confidence interval.<BR>\n" );
document.write( "At the intersection of this row and column is the value 2.064<BR>\n" );
document.write( "This value is approximate. To get more accuracy, you'll need to use the Tinv function on your calculator.\r<BR>\n" );
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document.write( "Margin of Error = (critical T value)*(standard deviation)/sqrt(sample size)<BR>\n" );
document.write( "Margin of Error = (2.064)*(7.2)/sqrt(25)<BR>\n" );
document.write( "Margin of Error = (2.064)*(7.2)/5<BR>\n" );
document.write( "Margin of Error = 14.8608/5<BR>\n" );
document.write( "<b><font size=4 color=red>Margin of Error = 2.97216</font></b> (which is approximate)\r<BR>\n" );
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document.write( "Side Note: the mean is not used at all to compute the margin of error.</font> </SPAN>\n" );
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