document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=771340>Question 771340</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Bulb has an average life of 600 hr. standard deviation of 30 hours. Length of bulb is approximated by a normal curve. A manager installs 10,000 bulbs. Find total number that can be expected to last less than 687 hours. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #470136 by </B><A HREF=/tutors/aboutme.mpl?userid=oscargut><B>oscargut(2103)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=oscargut><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/cgi-bin/show-face.mpl?user=oscargut><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=470136\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let X = life duration\r<BR>\n" );
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document.write( "X has a normal distribution with mean 600 and sd 30\r<BR>\n" );
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document.write( "Z = (x-600)/30 has a standard normal distribution \r<BR>\n" );
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document.write( "P(X<687) = P(Z<87/30) = P(Z<2.9) =0.99813\r<BR>\n" );
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document.write( "Then the expected number of bulbs is 10,000(0.99813) = 9981.3\r<BR>\n" );
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