document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=324064>Question 324064</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A standard placement test has a mean of 115 and a standard deviation of &#61555; = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of the true mean.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #231915 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=231915\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A standard placement test has a mean of 115 and a standard deviation of &#61555; = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of the true mean.<BR>\n" );
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document.write( "Since E = zs/sqrt(n)<BR>\n" );
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document.write( "sqrt(n) = zs/E<BR>\n" );
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document.write( "So, n = [zs/E]^2<BR>\n" );
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document.write( "z for 90% CI = 1.645<BR>\n" );
document.write( "s = 10<BR>\n" );
document.write( "E = 2<BR>\n" );
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document.write( "n = [1.645*10/2]^2 = 68 when rounded up<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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