document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=619946>Question 619946</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Hi, I was wondering if I could get some help understanding how to do this question:\r<BR>\n" );
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document.write( "How long do new batteries last on a camping trip? n1 = 42 random small camp flashlights <BR>\n" );
document.write( "were fitted with brand 1 batteries and left on until the batteries failed. The sample mean <BR>\n" );
document.write( "lifetime was  x = 9.8 hours. Another n2 = 38 random small flashlights of the same model <BR>\n" );
document.write( "were fitted with brand II batteries and left on until the batteries failed. The sample mean for<BR>\n" );
document.write( "lifetimes was x = 8.1 hours. Historical data suggests that &#963;1 = 2.2 hours and &#963;2 = 3.5 hours.  Find a 90% confidence interval for the population difference      of lifetimes for <BR>\n" );
document.write( "these batteries. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #389866 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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=389866\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> How long do new batteries last on a camping trip? <BR>\n" );
document.write( "n1 = 42 random small camp flashlights were fitted with brand 1 batteries and left on until the batteries failed. <BR>\n" );
document.write( "The sample mean lifetime was x = 9.8 hours. <BR>\n" );
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document.write( "Another n2 = 38 random small flashlights of the same model <BR>\n" );
document.write( "were fitted with brand II batteries and left on until the batteries failed. The sample mean forlifetimes was x = 8.1 hours. <BR>\n" );
document.write( "Historical data suggests that &#963;1 = 2.2 hours and &#963;2 = 3.5 hours. <BR>\n" );
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document.write( "Find a 90% confidence interval for the population difference of lifetimes for <BR>\n" );
document.write( "these batteries.<BR>\n" );
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document.write( "I used the 2-SampleZInterval function on my TI-84 to get this 90% conf. int.:<BR>\n" );
document.write( "(0.6119 , 2.7881)<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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document.write( " </SPAN>\n" );
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