document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=117057>Question 117057</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A computer is infected with a virus, assume that it infects 20 other computers within 5 minutes, and that these pc's and servers each infect 20 more machines within another 5minutes, etc. How long until 100million computers are infected </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #85136 by </B><A HREF=/tutors/aboutme.mpl?userid=edjones><B>edjones(8007)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=edjones><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=edjones><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=85136\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The is a geometric sequence.<BR>\n" );
document.write( "S(n)=a(1)((1-r^n)/(1-r)) sum of a finite geometric sequence.<BR>\n" );
document.write( "Since a(1)=1 we can leave it out without changing the result.<BR>\n" );
document.write( "r=20<BR>\n" );
document.write( "When n=7.131853 by my TI-89 calculator S(n)=100,000,000<BR>\n" );
document.write( "7.13*5=35.65<BR>\n" );
document.write( "So, by 36 minutes 100,000,000 computers are infected.<BR>\n" );
document.write( ".<BR>\n" );
document.write( "Ed </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );