document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=930921>Question 930921</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Suppose, as is roughly true, the number of hours per week ninth-grade students spend playing video games is distributed normally with a mean of 16.8 hours and a standard deviation of 3.6 hours.\r<BR>\n" );
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document.write( "what is the probability that a single randomly selected ninth-grader spends more than 21 hours each week playing video games?\r<BR>\n" );
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document.write( "what is the probability the average of 6 randomly selected ninth-graders spend more than 21 hours each week playing video games?\r<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 #565344 by </B><A HREF=/tutors/aboutme.mpl?userid=ewatrrr><B>ewatrrr(24785)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ewatrrr><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=ewatrrr><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=565344\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> mean of 16.8 hours and a standard deviation of 3.6 hours. <BR>\n" );
document.write( "P(a single randomly selected ninth-grader spends more than 21 hours )<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=z+=+blue%28x+-+mu%29%2Fblue%28sigma%29 ALIGN=MIDDLE  ALT=\"z+=+blue%28x+-+mu%29%2Fblue%28sigma%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >    <BR>\n" );
document.write( "P(x > 21) = p(z > 4.2/3.6) = P(z > 1.6667) = normalcdf(1.6667, 100) = .0478<BR>\n" );
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document.write( "P(the average of 6 randomly selected ninth-graders spend more than 21 hours )<BR>\n" );
document.write( " <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=z+=blue+%28x+-+mu%29%2Fblue%28sigma%2Fsqrt%28n%29%29 ALIGN=MIDDLE  ALT=\"z+=blue+%28x+-+mu%29%2Fblue%28sigma%2Fsqrt%28n%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "P( xbar > 21) = P( z > 4.2/(3.6/sqrt(6)) = P(z > 2.8577)= normalcdf(2.8577, 100)= .0021<BR>\n" );
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