document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=335567>Question 335567</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The usual life of a computer terminal at a university computer center is known to be normally distributed with a mean of 3.25 years and a standard deviation of .5 years.\r<BR>\n" );
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document.write( "A. What proportion of computer terminals will have a useful life of at least 3 years?<BR>\n" );
document.write( "B. Historically, 20% of the terminals have had a useful life less than the manufacture's advertised life. What is the manufacture's advertised life for the computer terminals?  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #240573 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=240573\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\">  The usual life of a computer terminal at a university computer center is known to be normally distributed with a mean of 3.25 years and a standard deviation of .5 years. <BR>\n" );
document.write( "A. What proportion of computer terminals will have a useful life of at least 3 years?<BR>\n" );
document.write( "z(3) = (3-3.25)/0.5 = -1/2<BR>\n" );
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document.write( "P(x >= 3) = P(z > -1/2) = normalcdf(-1/2,1000) = 0.6915<BR>\n" );
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document.write( "B. Historically, 20% of the terminals have had a useful life less than the manufacture's advertised life. What is the manufacture's advertised life for the computer terminals<BR>\n" );
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document.write( "Draw a normal curve with u = 3.25<BR>\n" );
document.write( "Find a point that has 20% of the population below 3.25<BR>\n" );
document.write( "That point has a left-tail of 30%.<BR>\n" );
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document.write( "Find the z-value with a 30% left-tail.<BR>\n" );
document.write( "invNorm(0.30) = -0.5244<BR>\n" );
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document.write( "Find the corresponding raw score value:<BR>\n" );
document.write( "x = zs+u<BR>\n" );
document.write( "x = -0.5244*0.5+3.25<BR>\n" );
document.write( "x = 2.9878<BR>\n" );
document.write( "====================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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