document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1150274>Question 1150274</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Suppose that a market research firm is hired to estimate the percent<BR>\n" );
document.write( "of adults living in a large city who have cell phones. 600 randomly selected<BR>\n" );
document.write( "adult residents in this city are surveyed to determine whether they have cell<BR>\n" );
document.write( "phones. Of the 600 people surveyed, 451 responded yes - they own cell phones.<BR>\n" );
document.write( "Using a 90% confidence level, compute a confidence interval estimate for the true proportion of adults residents of this city who have cell phones and interpret<BR>\n" );
document.write( "the confidence interval. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #773051 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=773051\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> 90% CI has z=1.645<BR>\n" );
document.write( "p hat is 451/600=0.752<BR>\n" );
document.write( "half interval for a 1 sample proportion is z*sqrt(p*(1-p)/n); sqrt (0.751*0.249/600)=0.01765<BR>\n" );
document.write( "z*se=0.029<BR>\n" );
document.write( "90% CI=(0.723, 0.781)<BR>\n" );
document.write( "We don't know the true value, but we can be 90% confident it is in that interval. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );