document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1180992>Question 1180992</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The lifetime in hours of a brand of light bulb is normally distributed with a mean of 221 hours and a standard deviation of 7 hours.  <BR>\n" );
document.write( "a) What is the probability that a light bulb lasts between 215 and 234 hours?<BR>\n" );
document.write( "b) What is the lifetime of a light bulb that is at the 85th percentile?<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 #810793 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=810793\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> mean is 221 hours.<BR>\n" );
document.write( "standard deviation is 7 hours.\r<BR>\n" );
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document.write( "a) What is the probability that a light bulb lasts between 215 and 234 hours?\r<BR>\n" );
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document.write( "the probability is .7727, using the calculator that can be found at <a  rel=nofollow HREF= \"https://davidmlane.com/hyperstat/z_table.html\" target = \"_blank\">https://davidmlane.com/hyperstat/z_table.html</a>\r<BR>\n" );
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document.write( "here's a display of the use of that calculator to solve this problem.\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" src = \"http://theo.x10hosting.com/2021/052601.jpg\">\r<BR>\n" );
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document.write( "b) What is the lifetime of a light bulb that is at the 85th percentile?\r<BR>\n" );
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document.write( "the lifetime of a bulb at the 85th percentile is 228.255, using the same calculator as above, only using the value from an area option rather than the area from a value option as was done solving the previous question.\r<BR>\n" );
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document.write( "here's a display of the use of that calculator to solve this problem.\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" src = \"http://theo.x10hosting.com/2021/052602.jpg\">\r<BR>\n" );
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document.write( "the 85th percentile means the lifetime of the bulb is greater than 85% of all the bulbs.\r<BR>\n" );
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