document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=259857>Question 259857</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Light bulbs are measured in lumens (light output), watts (energy used), and hours (life).  A soft white light bulb has a mean life of 700 hours and a standard deviation of 35 hours.  Julia claims that the soft light bulbs she uses give a mean life of 800 hours.  Use the z-score approach to test wether her claim is true or not. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #191343 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=191343\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Light bulbs are measured in lumens (light output), watts (energy used), and hours (life). <BR>\n" );
document.write( "A soft white light bulb has a mean life of 700 hours and a standard deviation of 35 hours. <BR>\n" );
document.write( "Julia claims that the soft light bulbs she uses give a mean life of 800 hours. Use the z-score approach to test whether her claim is true or not.<BR>\n" );
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document.write( "Find the probability the life is >= 800 if u = 700 and sigma = 35<BR>\n" );
document.write( "z(800) = (800-700)/35 = 2.857<BR>\n" );
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document.write( "P(life >=800) = P(z > 2.857) = 0.0021...<BR>\n" );
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document.write( "Chances are 2 out of a thousand that Julia is correct.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );