document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=218807>Question 218807</A>: <I><SPAN STYLE=\"word-break: break-all;\"> What is the units digit of 3^1 + 3^3 + 3^5 + 3^7 +………+ 3^2009 ? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #164720 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><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=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=164720\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> What is the units digit of 3^1 + 3^3 + 3^5 + 3^7 +………+ 3^2009 ?<BR>\n" );
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document.write( "The units digit for powers of 3 is cyclic.  It goes:<BR>\n" );
document.write( "3, 9, 7, 1, 3, 9, 7, 1 ...<BR>\n" );
document.write( "The sequence above is 3,7,3,7, etc  Each pair adds to 0.<BR>\n" );
document.write( "2009 modulo 4 = 1<BR>\n" );
document.write( "The units digit of the sum is 3.<BR>\n" );
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