document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1110216>Question 1110216</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Given the sequence 3;6;9;....;60.\r<BR>\n" );
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document.write( "a)Determine the sum of all the natural numbers from 1 to 60 which are not multiples of 3.<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #725234 by </B><A HREF=/tutors/aboutme.mpl?userid=math_helper><B>math_helper(2461)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=math_helper><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=math_helper><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=725234\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <BR>\n" );
document.write( "The key to solve this is to recall that  Sum(1,2,…, N) =  N*(N+1)/2\r<BR>\n" );
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document.write( "Sum(3,6,9,…,60) = 3*Sum(1,2,3,…,20) = 3*(20*21/2) = 630<BR>\n" );
document.write( "Sum(1,2,3,…,60) = 61*60/2 = 1830\r<BR>\n" );
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document.write( "Sum of natural numbers which are not multiples of 3:  1830-630 = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=+highlight%28+1200+%29+ ALIGN=MIDDLE  ALT=\"+highlight%28+1200+%29+\"   DISABLED_style= \"max-width:90%; height:auto;\" > </SPAN>\n" );
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