document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1168750>Question 1168750</A>: <I><SPAN STYLE=\"word-break: break-all;\"> You measure 30 textbooks' weights, and find they have a mean weight of 78 ounces. Assume the population standard deviation is 2.3 ounces. Based on this, construct a 99% confidence interval for the true population mean textbook weight.\r<BR>\n" );
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document.write( "Give your answers as decimals, to two places\r<BR>\n" );
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document.write( "<  μ <  </SPAN>\n" );
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document.write( "Given information:<BR>\n" );
document.write( "mean = xbar = 78<BR>\n" );
document.write( "standard deviation = sigma = 2.3<BR>\n" );
document.write( "sample size = n = 30<BR>\n" );
document.write( "confidence level = 99%\r<BR>\n" );
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document.write( "A 99% confidence level means the critical value is approximately z = 2.58 which you find using a calculator or table.\r<BR>\n" );
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document.write( "The lower value of the confidence interval is<BR>\n" );
document.write( "L = xbar - z*sigma/sqrt(n)<BR>\n" );
document.write( "L = 78 - 2.58*2.3/sqrt(30)<BR>\n" );
document.write( "L = 78 - 1.083395<BR>\n" );
document.write( "L = 76.916605<BR>\n" );
document.write( "L = 76.92\r<BR>\n" );
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document.write( "The upper value of the confidence interval is<BR>\n" );
document.write( "U = xbar + z*sigma/sqrt(n)<BR>\n" );
document.write( "U = 78 + 2.58*2.3/sqrt(30)<BR>\n" );
document.write( "U = 78 + 1.083395<BR>\n" );
document.write( "U = 79.083395<BR>\n" );
document.write( "U = 79.08\r<BR>\n" );
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document.write( "The 99% confidence interval is therefore<BR>\n" );
document.write( "76.92 < μ < 79.08\r<BR>\n" );
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