document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1067247>Question 1067247</A>: <I><SPAN STYLE=\"word-break: break-all;\"> the lifetimes of a brand of electric light bulbs are normally distributed with mean 1300hours  and standartd deviation 120hours. a light bulb is selected at random and tested by keeping it on continuously \r<BR>\n" );
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document.write( "find the probability that it has a lifetime of over 1540hours?\r<BR>\n" );
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document.write( "its has a lifetime between 1222 and 1540 hours?\r<BR>\n" );
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document.write( "two light bulbs are selected at random.<BR>\n" );
document.write( "find the probability that they both last between 1222 and 1540<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 #682454 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=682454\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> z=(x-mean)/sd<BR>\n" );
document.write( "=(1540-300/120=2<BR>\n" );
document.write( "probability z>2=0.0228<BR>\n" );
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document.write( "(1222-1300)/120=-78/120=-0.65<BR>\n" );
document.write( "probability -0.65<z<2=0.7194<BR>\n" );
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document.write( "That would be the probability just obtained squared, since they are independent: 0.5175 if I don't round the last one. </SPAN>\n" );
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