document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1209780>Question 1209780</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Evaluate 21 + 27 + 33 + ... + 261 + 267 + 273 + ... + 6021. </SPAN>\n" );
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document.write( "21+27+33+...+6021<br><BR>\n" );
document.write( "The common difference is 6, so the formula for the n-th term is of the form<br><BR>\n" );
document.write( "t(n) = 6n+b<br><BR>\n" );
document.write( "t(1) = 21, so the formula is<br><BR>\n" );
document.write( "t(n) = 6n+15<br><BR>\n" );
document.write( "The last term is 6021:<br><BR>\n" );
document.write( "6n+15 = 6021<BR>\n" );
document.write( "6n = 6006<BR>\n" );
document.write( "n = 1001<br><BR>\n" );
document.write( "The sequence is 1001 terms with first term 21 and last term 6021.<br><BR>\n" );
document.write( "Sum = (number of terms) * (average of all the terms) = (number of terms) * (average of first and last terms)<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%281001%29%28%2821%2B6021%29%2F2%29=%281001%29%283021%29=3021000%2B3021=3024021 ALIGN=MIDDLE  ALT=\"%281001%29%28%2821%2B6021%29%2F2%29=%281001%29%283021%29=3021000%2B3021=3024021\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "ANSWER: 3024021<br><BR>\n" );
document.write( " </SPAN>\n" );
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