document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=134678>Question 134678</A>: <I><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<BR>\n" );
document.write( "(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:<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" );
document.write( "(a) Construct a 95 percent confidence interval for the true mean. (b) Why might normality be an<BR>\n" );
document.write( "issue here? (c) What sample size would be needed to obtain an error of ±10 square millimeters<BR>\n" );
document.write( "with 99 percent confidence? (d) If this is not a reasonable requirement, suggest one that is. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #98532 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=98532\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The data (in<BR>\n" );
document.write( "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" );
document.write( "(a) Construct a 95 percent confidence interval for the true mean.<BR>\n" );
document.write( "x-bar = 346.5<BR>\n" );
document.write( "E = 1.96*170.3784/sqrt(20)= 0.0514<BR>\n" );
document.write( "CI: 346.5-0.0514 < mu < 346.5+0.0514<BR>\n" );
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document.write( "(b) Why might normality be an issue here?<BR>\n" );
document.write( "The population goes far beyond one phone directory.<BR>\n" );
document.write( "----------------------------------------- <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( "E = z*sigma/sqrt(n)<BR>\n" );
document.write( "n = [z*sigma/E]^2<BR>\n" );
document.write( "n = [1.96*170.3784/10]^2 = 1115.17<BR>\n" );
document.write( "n rounded up = 1116<BR>\n" );
document.write( "--------------------------- <BR>\n" );
document.write( "(d) If this is not a reasonable requirement, suggest one that is.<BR>\n" );
document.write( "I'll leave that to you.<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );