document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=314396>Question 314396</A>: <I><SPAN STYLE=\"word-break: break-all;\"> # 1.) The weight of full boxes of frosted Mini-wheat cereal are normally distributed with a standard deviation of 0.52 oz. A sample of 18 randomly selected boxes produced a mean weight of 24.3 oz. Find the 95% confidence interval for the true mean weight of a box of this cereal.\r<BR>\n" );
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document.write( "# 2.) We are interested in estimating the mean life of a new product. How large a sample do we need to take in order to estimate the mean to within 0.20 of a standard deviation with 90% confidence? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #224761 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=224761\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> # 1.) The weight of full boxes of frosted Mini-wheat cereal are normally distributed with a standard deviation of 0.52 oz. A sample of 18 randomly selected boxes produced a mean weight of 24.3 oz. Find the 95% confidence interval for the true mean weight of a box of this cereal.<BR>\n" );
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document.write( "sample mean: 24.3<BR>\n" );
document.write( "E = [invT(0.975 with df = 17)]*0.52/sqrt(18) = 2.1098*0.1226 = 0.2586<BR>\n" );
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document.write( "95% CI: 24.3-0.2596 < u < 24.3+0.2596<BR>\n" );
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document.write( "# 2.) We are interested in estimating the mean life of a new product. How large a sample do we need to take in order to estimate the mean to within 0.20 of a standard deviation with 90% confidence?<BR>\n" );
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document.write( "n = [z*s/E]^2<BR>\n" );
document.write( "n = [1.645*s/0.2]^2<BR>\n" );
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document.write( "Note: You need to know the standard deviation.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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