document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1086483>Question 1086483</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A study of nickels showed that the standard deviation of the weight of nickels is 150 milligrams. A coin counter manufacturer wishes to find the 80% confidence interval for the average weight of a nickel. How many nickels does he need to weigh to obtain an average accurate to within 10 milligrams?<BR>\n" );
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document.write( "a. 225<BR>\n" );
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document.write( "b. 369<BR>\n" );
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document.write( "c. 613<BR>\n" );
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document.write( "d. 159<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #700686 by </B><A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><B>jim_thompson5910(35256)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jim_thompson5910><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=700686\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=\"black\" face=\"times\" size=\"3\">We will use this formula<BR>\n" );
document.write( "n = ( (z*sigma)/E )^2\r<BR>\n" );
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document.write( "The variables are<BR>\n" );
document.write( "n = sample size<BR>\n" );
document.write( "z = critical value<BR>\n" );
document.write( "sigma = population standard deviation<BR>\n" );
document.write( "E = margin of error<BR>\n" );
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document.write( "Use a table or calculator to find that<BR>\n" );
document.write( "Critical value = z = 1.28 (at 80% confidence)\r<BR>\n" );
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document.write( "In this case, we're given<BR>\n" );
document.write( "sigma = 150<BR>\n" );
document.write( "E = 10\r<BR>\n" );
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document.write( "Plug those values into the formula to get:<BR>\n" );
document.write( "n = ( (z*sigma)/E )^2<BR>\n" );
document.write( "n = ( (1.28*150)/10 )^2<BR>\n" );
document.write( "n = ( 192/10 )^2<BR>\n" );
document.write( "n = ( 19.2 )^2<BR>\n" );
document.write( "n = 368.64<BR>\n" );
document.write( "n = 369 ... round up to the nearest whole number\r<BR>\n" );
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document.write( "Final answer is choice B) 369</font> </SPAN>\n" );
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