document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=221674>Question 221674</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The new Twinkle bulb has a standard deviation 34 hours. A random sample of 77 light bulbs is selected from inventory. The sample mean was found to be 492 hours. Find the margin of error E for a 90% confidence interval. Round your answer to the nearest hundredths. Then I have to construct a 90% confidence interval for the mean life. I know how to do that part I just can't figure out the first part. The sqrt gets me.      </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #166210 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=166210\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The new Twinkle bulb has a standard deviation 34 hours. <BR>\n" );
document.write( "A random sample of 77 light bulbs is selected from inventory. <BR>\n" );
document.write( "The sample mean was found to be 492 hours. \r<BR>\n" );
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document.write( "Find the margin of error E for a 90% confidence interval. Round your answer to the nearest hundredths. \r<BR>\n" );
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document.write( "Then I have to construct a 90% confidence interval for the mean life. \r<BR>\n" );
document.write( "\n" );
document.write( "I know how to do that part I just can't figure out the first part. The sqrt gets me. <BR>\n" );
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document.write( "invT(0.05,76) = -1.6652<BR>\n" );
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document.write( "E = 1.6652[34/sqrt(77)] = 6.4519<BR>\n" );
document.write( "-------------------------------------------<BR>\n" );
document.write( "90% CI: 492 - 6.4519 < u < 492 + 6.4519<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );