document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=737156>Question 737156</A>: <I><SPAN STYLE=\"word-break: break-all;\"> To see whether people are keeping their car tires inflated to the correct level of 35 pounds per square inch (psi), a tire company manager selects a sample of 36 tires and checks the pressure. The mean of the sample is 33.5 psi, and the population standard deviation is 3 psi. Are the tires properly inflated? Use a=.10. Find the 90% confident interval of the mean. Do the results agree? Explain? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #450224 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=450224\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  To see whether people are keeping their car tires inflated to the correct level of 35 pounds per square inch (psi), a tire company manager selects a sample of 36 tires and checks the pressure. <BR>\n" );
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document.write( "The mean of the sample is 33.5 psi, and the population standard deviation is 3 psi. <BR>\n" );
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document.write( "Are the tires properly inflated? Use a=.10.<BR>\n" );
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document.write( "Ho: u = 35<BR>\n" );
document.write( "Ha: u # 35<BR>\n" );
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document.write( "x-bar = 33.5<BR>\n" );
document.write( "z(33.5) = (33.5-35)/[3/sqrt(36)] = -3<BR>\n" );
document.write( "p-value = 2*P(z < -3) = 2*normalcdf(-100,-3) = 0.0027<BR>\n" );
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document.write( "Since the p-value is less than 10%, reject Ho. <BR>\n" );
document.write( "The test results do not support the tires being properly inflated.<BR>\n" );
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document.write( "Find the 90% confident interval of the mean. Do the results agree?<BR>\n" );
document.write( "Using my Ti-84 I get:<BR>\n" );
document.write( "90% CI: (32.678,34.3220<BR>\n" );
document.write( "Since 35 is not in the 90% confidence interval the test does not<BR>\n" );
document.write( "support proper inflation at the 10% level of significance level.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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