document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=224172>Question 224172</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I am looking for some general help in understanding this concept concerning confidence intervals.  I have a file where I have used the data in the spread sheet to find the mean, standard deviation, and some other point estimates.  Now I am trying to determine the next step to find the answers to the following questions:\r<BR>\n" );
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document.write( "Find the 90% CI for the portion of all customers whose order is more than $85 (since this is a population portion problem I chose to count the number of people whose order is over $85/number in sample to determine phat) Am I on the right track?  I want to do something similar for the other part of the question.\r<BR>\n" );
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document.write( "Find the 95% Confidence Interval for the portion of all customers whose order contains at least 3 items and cost at least $85 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #167481 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=167481\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Find the 90% CI for the portion of all customers whose order is more than $85 (since this is a population portion problem I chose to count the number of people whose order is over $85/number in sample to determine phat) Am I on the right track? I want to do something similar for the other part of the question.<BR>\n" );
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document.write( "Your sample size is \"n\". The number whose order is > $85.<BR>\n" );
document.write( "The sample proportion is x/n<BR>\n" );
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document.write( "Find the z-value associated with a 90% two-tail: z = 1.645<BR>\n" );
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document.write( "Find the \"standard error\" = E = 1.645*sigma/sqrt(n)<BR>\n" );
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document.write( "The 90% CI is (p-hat - E , p-hat+E)<BR>\n" );
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document.write( "and <BR>\n" );
document.write( "Find the 95% Confidence Interval for the proportion of all customers whose order contains at least 3 items and cost at least $85<BR>\n" );
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document.write( "Same as above but use the z-value associated with a 95% two-tail: z = 1.96<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H> </SPAN>\n" );
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