document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=370437>Question 370437</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Life of Light Bulbs A certain type of light bulb has an average<BR>\n" );
document.write( "life of 500 hours, with a standard deviation of 100 hours. The<BR>\n" );
document.write( "length of life of the bulb can be closely approximated by a normal<BR>\n" );
document.write( "curve. An amusement park buys and installs 10,000 such<BR>\n" );
document.write( "bulbs. Find the total number that can be expected to last for<BR>\n" );
document.write( "each period of time.\r<BR>\n" );
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document.write( "Q:Find the shortest and longest lengths of life for the middle<BR>\n" );
document.write( "80% of the bulbs.<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 #264042 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=264042\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Life of Light Bulbs A certain type of light bulb has an average<BR>\n" );
document.write( "life of 500 hours, with a standard deviation of 100 hours. The<BR>\n" );
document.write( "length of life of the bulb can be closely approximated by a normal<BR>\n" );
document.write( "curve. An amusement park buys and installs 10,000 such<BR>\n" );
document.write( "bulbs. Find the total number that can be expected to last for<BR>\n" );
document.write( "each period of time. \r<BR>\n" );
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document.write( "Q:Find the shortest and longest lengths of life for the middle<BR>\n" );
document.write( "80% of the bulbs.<BR>\n" );
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document.write( "The middle 80% has a left tail of 10% and a right tail of 10%<BR>\n" );
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document.write( "The z-value with a left tail of 10% = -1.2816<BR>\n" );
document.write( "The z-value with a right tail of 10% = 1.2816<BR>\n" );
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document.write( "Life cutoff for the lowest 10% = -1.2816*100+500 = 372 hrs.<BR>\n" );
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document.write( "Life cutoff for the top 10% = 1.2816*100+500 = 628 hrs\r<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.\r<BR>\n" );
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