document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=307267>Question 307267</A>: <I><SPAN STYLE=\"word-break: break-all;\"> In mathematics, n! means the product of the numbers from 1 to n.<BR>\n" );
document.write( "For example, 3! = 1 × 2 × 3. Determine the one’s digit of the sum\r<BR>\n" );
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document.write( "1! + 2! + 3! + · · · + 18! + 19! + 20!\r<BR>\n" );
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document.write( "a 0   b 3   c 5   d 7    e 9 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #219844 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=219844\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> 1! = 1<BR>\n" );
document.write( "2! = 1! * 2 = 1 * 2 = 2<BR>\n" );
document.write( "3! = 2! * 3 = 2 * 3 = 6<BR>\n" );
document.write( "4! = 3! * 4 = 6 * 4 = 24<BR>\n" );
document.write( "5! = 4! * 5 = 24 * 5 = 720<BR>\n" );
document.write( "6! = 5! * 6 = 720 * 6 = 4320<BR>\n" );
document.write( "7! = 6! * 7 = 4320 * 7 = 30240\r<BR>\n" );
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document.write( "Once the units digit becomes 0, it will remain 0 forever because any number times 0 will always equal 0.\r<BR>\n" );
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document.write( "The units digit of the sum will remain what it is after you reach 4!.\r<BR>\n" );
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document.write( "1! + 2! + 3! + 4! = 1 + 2 + 6 + 24 = 33\r<BR>\n" );
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document.write( "The units digit of the sum of the factorials is 3 and will remain 3 forever.\r<BR>\n" );
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document.write( "That would be selection B.\r<BR>\n" );
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document.write( " </SPAN>\n" );
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