document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1104551>Question 1104551</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Please help me solve this word problem:\r<BR>\n" );
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document.write( "in 1991, the average cost of attending a public university through graduation. Was $20,972. If johns parents deposited that amount in an account in 1991 at an interest rate of 7% compounded semi-annually, how long will it take for the money to double? Round answer to two decimals. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #720199 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=720199\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> P=Po(1+r/2)^2t, t is years<BR>\n" );
document.write( "Any amount to double is where P=2Po<BR>\n" );
document.write( "so 2=(1+0.035)^2t<BR>\n" );
document.write( "ln2=2t ln(1.035)<BR>\n" );
document.write( "2t=ln 2/ln (1.035)<BR>\n" );
document.write( "t=10.07 years<BR>\n" );
document.write( "as a rough check, the rule of 72 would predict 10.29 years. </SPAN>\n" );
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