document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1180510>Question 1180510</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Recent research suggests that Americans make an average of 10 phone calls per<BR>\n" );
document.write( "day. Let the number of calls be normally distributed with a standard deviation of 3 calls.<BR>\n" );
document.write( "Compute the probability that an average American makes phone calls between 4 and 12<BR>\n" );
document.write( "calls per day.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #810228 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=810228\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> z=(x-mean)/sd<BR>\n" );
document.write( "so the lower bound is (4-10)/3 or -2<BR>\n" );
document.write( "and the upper bound is (12-10)/3 or +2/3<BR>\n" );
document.write( "The probability for z between those two numbers is 0.7248 </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );