document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1159791>Question 1159791</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The lifetime of a certain brand of battery is known to have a standard deviation of 11.5 hours. Suppose that a random sample of 80 such batteries has a mean lifetime of 43.9 hours. Based on this sample, find a 99% confidence interval for the true mean lifetime of all batteries of this brand.\r<BR>\n" );
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document.write( "Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.\r<BR>\n" );
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document.write( "What is the lower limit of the 99% confidence interval?	<BR>\n" );
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document.write( "What is the upper limit of the 99% confidence interval?	 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #782872 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=782872\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> half-interval is z(0.995)*sigma/sqrt(n)<BR>\n" );
document.write( "=2.576*11.5/sqrt(80)<BR>\n" );
document.write( "=3.31\r<BR>\n" );
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document.write( "99% CI is mean+/- margin of error<BR>\n" );
document.write( "(40.6, 47.2) hours  </SPAN>\n" );
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