document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=148331>Question 148331</A>This question is from textbook <A HREF=http://www.amazon.com/exec/obidos/ASIN/9780072966930/algebrahomeworkh></A><BR>\n" );
document.write( ": <I><SPAN STYLE=\"word-break: break-all;\"> Probability is not my high point. I have tried to come up with an answer, but I need assistance, please. Here is the question:\r<BR>\n" );
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document.write( "A sample of 20 pages was taken without replacement from the 1,591-page phone directory<BR>\n" );
document.write( "Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in<BR>\n" );
document.write( "square millimeters) are shown below:\r<BR>\n" );
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document.write( "0 260 356 403 536 0 268 369 428 536<BR>\n" );
document.write( "268 396 469 536 162 338 403 536 536 130\r<BR>\n" );
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document.write( "(a) Construct a 95 percent confidence interval for the true mean. <BR>\n" );
document.write( "(b) Why might normality be an issue here?<BR>\n" );
document.write( "(c) What sample size would be needed to obtain an error of ±10 square millimeters with 99 percent confidence? <BR>\n" );
document.write( "(d) If this is not a reasonable requirement, suggest one that is.\r<BR>\n" );
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document.write( "Thank you! </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #108773 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=108773\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A sample of 20 pages was taken without replacement from the 1,591-page phone directory<BR>\n" );
document.write( "Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). <BR>\n" );
document.write( "The data (in square millimeters) are shown below: <BR>\n" );
document.write( "0 260 356 403 536 0 268 369 428 536<BR>\n" );
document.write( "268 396 469 536 162 338 403 536 536 130<BR>\n" );
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document.write( "x-bar = 346.5 ; s = 170.378 <BR>\n" );
document.write( "(a) Construct a 95 percent confidence interval for the true mean.<BR>\n" );
document.write( "I'm assuming you want a Z-Interval:<BR>\n" );
document.write( "E = 1.96[170.378/sqrt(20] = 74.6715<BR>\n" );
document.write( "95% CI: (x-bar-E, x-bar+E) = (346.5-74.6715 , 346.5+74.6715)<BR>\n" );
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document.write( "(b) Why might normality be an issue here?<BR>\n" );
document.write( "These 20 samples gathered in the way described is probably not a random<BR>\n" );
document.write( "sample.<BR>\n" );
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document.write( "(c) What sample size would be needed to obtain an error of ±10 square millimeters with 99 percent confidence?<BR>\n" );
document.write( "E = z<BR>\n" );
document.write( "n = [2.326s/E]^2<BR>\n" );
document.write( "n = [2.326*170.378/10]^2 = 1571 when rounded up.<BR>\n" );
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document.write( "(d) If this is not a reasonable requirement, suggest one that is.<BR>\n" );
document.write( "You would get a smaller \"n\" if you increase the size of E or <BR>\n" );
document.write( "decrease the size of z* by requiring less confidence.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.\r<BR>\n" );
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document.write( " </SPAN>\n" );
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