document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1128745>Question 1128745</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The lengths of pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days.  Out of 50 pregnancies how many would you expect to last less than 250 days? My answer was -14.53.  I do not believe it is correct.  Please help, and thank you.\r<BR>\n" );
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document.write( "The lengths of pregnancies of human are normally distributed with a mean of 268 days and a standard deviation of 15 days. A baby is premature if it is born three weeks early. What percent of babies are born prematurely? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #745291 by </B><A HREF=/tutors/aboutme.mpl?userid=rothauserc><B>rothauserc(4718)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rothauserc><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=rothauserc><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=745291\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> z-score = (250 - 268) / 15 = -1.2<BR>\n" );
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document.write( "the probability(P) associated with a z-score of -1.2 is determined from the table of z-scores<BR>\n" );
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document.write( "P(X < 250) = 0.1151<BR>\n" );
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document.write( "50 * 0.1151 = 5.755 is approximately 6 pregnancies less than 250 days<BR>\n" );
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document.write( "268 - (7 * 3) = 247 days<BR>\n" );
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document.write( "we use the normal distribution to approximate 247<BR>\n" );
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document.write( "P(X = 247) = P(X < 247.5) - P(X < 246.5)<BR>\n" );
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document.write( "z-score(247.5) = (247.5 - 268) / 15 is approximately -1.37<BR>\n" );
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document.write( "z-score(246.5) = (246.5 - 268) / 15 is approximately -1.43<BR>\n" );
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document.write( "P(X = 247) = 0.0853 - 0.0764 = 0.0089 is approximately 1%<BR>\n" );
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