document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1052345>Question 1052345</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Let x be a random variable that represents white blood cell count per cubic milliliter of whole blood. Assume that x has a distribution that is approximately normal, with mean &#956; = 7100 and estimated standard deviation &#963; = 2450. A test result of x < 3500 is an indication of leukopenia. This indicates bone marrow depression that may be the result of a viral infection.\r<BR>\n" );
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document.write( "(a) What is the probability that, on a single test, x is less than 3500? (Round your answer to four decimal places.)<BR>\n" );
document.write( "(b) What is the probability of x < 3500? (Round your answer to four decimal places.) <BR>\n" );
document.write( "(c) Repeat part (b) for n = 3 tests taken a week apart. (Round your answer to four decimal places.) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #667712 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=667712\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> z=(x-mean)/sd<BR>\n" );
document.write( "=(3500-7100)/2450=-3500/2450=-1.43<BR>\n" );
document.write( "probability x<3500 is probability z<-1.43, which is 0.0764.<BR>\n" );
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document.write( "For b, I get the same thing.  I am not clear how this is different.<BR>\n" );
document.write( "I am not certain what they mean by c.<BR>\n" );
document.write( "If it is the probability that all 3 tests are <3500, it would be 0.0764^3, assuming independence, and that is 0.0004.\r<BR>\n" );
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document.write( "If it is the probability it happens at least once, then it is 1- probability it doesn't happen three times in a row, which is (1)-(0.9236)^3= 1-(0.7874)=0.2126. </SPAN>\n" );
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