document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1168670>Question 1168670</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A medical researcher wants to investigate the amount of times it takes for patients’ headache pain to be relived after taking a new prescription painkiller. She plans to use statistical methods to estimate the mean of the population of relief times. She believes that the population is normally distributed with a standard deviation of 23 minutes. How large a sample should she take to estimate the mean time to within 3 minutes with 99% confidence?  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #793237 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=793237\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> half-interval is 3 minutes=z(0.995)*sigma/sqrt(n), z=2.576 sigma is 23<BR>\n" );
document.write( "so 3=2.576*23/sqrt(n)<BR>\n" );
document.write( "sqrt(n)=2.5758*23/3=19.749<BR>\n" );
document.write( "n=390 people\r<BR>\n" );
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document.write( "note, if one uses 2.576 for z, the answer it 390.03 and that would be rounded up to 391. </SPAN>\n" );
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