document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=229988>Question 229988</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The daily cost of photocopying in a certain office is assumed to be normally distributed with a mean of $80 and a standard deviation of $4. Find the probability that:<BR>\n" );
document.write( "a) the cost for a randomly selected day is more than $75 -----> = 0.8944<BR>\n" );
document.write( "b) the average cost of 10 randomly selected days is more than $75\r<BR>\n" );
document.write( "\n" );
document.write( "Stuck with part b, should it just be 0.8944^10? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #170414 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=170414\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The daily cost of photocopying in a certain office is assumed to be normally distributed with a mean of $80 and a standard deviation of $4. Find the probability that:<BR>\n" );
document.write( "a) the cost for a randomly selected day is more than $75 -----> = 0.8944<BR>\n" );
document.write( "b) the average cost of 10 randomly selected days is more than $75 <BR>\n" );
document.write( "Stuck with part b, should it just be 0.8944^10?<BR>\n" );
document.write( "--------------------------<BR>\n" );
document.write( "Comment: Part \"a\" is a population problem where the mean is u and std = sigma<BR>\n" );
document.write( "Part \"b\" is a sample-means problem where the mean of the sample means is u but std = sigma/sqrt(n)<BR>\n" );
document.write( "-----------------------------<BR>\n" );
document.write( "Part \"b\":<BR>\n" );
document.write( "z(75) = (75-80)/(4/sqrt(10)) = -3.9528<BR>\n" );
document.write( "---<BR>\n" );
document.write( "P(x-bar > 75) = P(z > -3.9528) = 0.9999..<BR>\n" );
document.write( "---------------------------------------------------<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );