document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1068633>Question 1068633</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Passenger comfort is influenced by the amount of pressurization in an airline cabin. Higher pressurization allows a closer-to-normal environment and a more relaxed flight. A study by an airline user group recorded the corresponding air pressure on 30 randomly chosen flights. The study revealed a mean equivalent pressure of 8000 feet with a standard deviation of 300 feet.\r<BR>\n" );
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document.write( "    Develop a 99% confidence interval for the population mean equivalent pressure.\r<BR>\n" );
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document.write( "    How large a sample is needed to find the population mean within 25 feet at 95% confidence?<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 #683956 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=683956\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> CI is 8000+/-t df=29,0.995 *300/sqrt(30); t value is 2.756<BR>\n" );
document.write( "interval width is 2.756*300/sqrt(30)=150.95<BR>\n" );
document.write( "(7849,8151)<BR>\n" );
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document.write( "interval is 25=z*300/sqrt(n)<BR>\n" );
document.write( "I use z, because the sample size is large, and I can always then use t for that df and see if it changes the result.<BR>\n" );
document.write( "25=1.96*300/sqrt(n)<BR>\n" );
document.write( "25 sqrt(n)=1.96*300=588<BR>\n" );
document.write( "sqrt(n)=588/25=23.52<BR>\n" );
document.write( "square both sides<BR>\n" );
document.write( "n=553.19 round to 554. With this size sample, t=z.<BR>\n" );
document.write( "When I use this in the calculator for a t-test, I get an interval of +/-25. </SPAN>\n" );
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