document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=258380>Question 258380</A>: <I><SPAN STYLE=\"word-break: break-all;\"> On the first day, Joe joined a secret club as its only member. Each day after that, one more member joined than on the previous day. What was the membership of the club after 40 days?\r<BR>\n" );
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document.write( "((( I did this: 40 multiplied by 2 ; because it says each day after one more member joined than on the previous. So then I got 80 and added joe and got 81???))) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #190218 by </B><A HREF=/tutors/aboutme.mpl?userid=richwmiller><B>richwmiller(17219)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=richwmiller><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=richwmiller><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=190218\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> day joined membership<BR>\n" );
document.write( "0    0    0<BR>\n" );
document.write( "1 1 1<BR>\n" );
document.write( "2 2 3<BR>\n" );
document.write( "3 3 6<BR>\n" );
document.write( "4 4 10<BR>\n" );
document.write( "5 5 15<BR>\n" );
document.write( "6 6 21<BR>\n" );
document.write( "7 7 28<BR>\n" );
document.write( "8 8 36<BR>\n" );
document.write( "9 9 45<BR>\n" );
document.write( "10 10 55<BR>\n" );
document.write( "11 11 66<BR>\n" );
document.write( "12 12 78<BR>\n" );
document.write( "13 13 91\r<BR>\n" );
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document.write( "The new total  is the previous total plus the new day<BR>\n" );
document.write( "#8 is 36 which is 1/2*8*9<BR>\n" );
document.write( "#10 is 55 which is 1/2*10*11=55<BR>\n" );
document.write( "#12 78 1/2 12*13=6*13<BR>\n" );
document.write( "total = day*day+1*1/2<BR>\n" );
document.write( "It also works with odd numbers<BR>\n" );
document.write( "#11 11*12*1/2=66<BR>\n" );
document.write( "so we have <BR>\n" );
document.write( "t=d*(d+1)*1/2<BR>\n" );
document.write( "t=40*41*1/2<BR>\n" );
document.write( "t=20*41=820 after 40 days </SPAN>\n" );
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