document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1205253>Question 1205253</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A research firm conducted a survey to determine the mean amount smokers spend on cigarette during a week. A sample of 49 smokers revealed that the sample mean is Br. 20 with standard deviation of Br. 5. Construct 95% confidence interval for the mean amount spent. </SPAN>\n" );
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document.write( "At 95% confidence, the z critical value is roughly z = 1.96 which is something to memorize or have handy on a reference sheet somewhere.\r<BR>\n" );
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document.write( "n = 49 = sample size<BR>\n" );
document.write( "xbar = 20 = sample mean<BR>\n" );
document.write( "s = 5 = sample standard deviation\r<BR>\n" );
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document.write( "E = margin of error for the mean<BR>\n" );
document.write( "E = z*s/sqrt(n)<BR>\n" );
document.write( "E = 1.96*5/sqrt(49)<BR>\n" );
document.write( "E = 1.4\r<BR>\n" );
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document.write( "L = lower boundary of the confidence interval<BR>\n" );
document.write( "L = xbar - E<BR>\n" );
document.write( "L = 20 - 1.4<BR>\n" );
document.write( "L = 18.6\r<BR>\n" );
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document.write( "U = upper boundary of the confidence interval<BR>\n" );
document.write( "U = xbar + E<BR>\n" );
document.write( "U = 20 + 1.4<BR>\n" );
document.write( "U = 21.4\r<BR>\n" );
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document.write( "The 95% confidence interval is approximately 18.6 < mu < 21.4<BR>\n" );
document.write( "It's of the format L < mu < U.\r<BR>\n" );
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document.write( "We can condense that to the notation (18.6, 21.4)<BR>\n" );
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