document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1203420>Question 1203420</A>: <I><SPAN STYLE=\"word-break: break-all;\"> In a random selection of 64 of the 2400 intersections in a city, the mean number of car accidents per year was 3.2 and the sample standard deviation was 0.8. Obtain the 90% confidence interval for the mean number of accidents per intersection per year.<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #838973 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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/cgi-bin/show-face.mpl?user=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=838973\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> sample size is 64.<BR>\n" );
document.write( "mean number of car accidents per year was 3.2 and sample standard deviation was .8.\r<BR>\n" );
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document.write( "t-score is indicated because the standard deviatiion is from the sample rather than from the population.\r<BR>\n" );
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document.write( "90% two tailed confidence interval has critical t-score with 63 degrees of freedom (sample size minus 1) equal to plus or minus t = 1.6694.\r<BR>\n" );
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document.write( "raw score is based on t-score formula of t = (x-m)/s.<BR>\n" );
document.write( "t is the t-score.<BR>\n" );
document.write( "m is the population mean.<BR>\n" );
document.write( "s is the standard error.<BR>\n" );
document.write( "solve for x to get the raw score.\r<BR>\n" );
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document.write( "standard error = sample standard deviation / sqrt(sample size) = .8/sqrt(64) = .8/8 = .1.\r<BR>\n" );
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document.write( "on the low side of the confidence interval, you get -1.6694 = (x-3.2)/.1.<BR>\n" );
document.write( "solve for x to get x = .1 * -1.6694 + 3.2 = 3.03306.\r<BR>\n" );
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document.write( "on the high side of the confidence interval, you get 1.6694 = (x-3.2)/.1.<BR>\n" );
document.write( "solve for x to get x = .1 * 1.6694 + 3.2 = 3.36694.\r<BR>\n" );
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document.write( "your 90% confidence interval is 33.03306 to 3.36694.\r<BR>\n" );
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