document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=978611>Question 978611</A>: <I><SPAN STYLE=\"word-break: break-all;\"> An auditorium has 20 rows of seats. The first row contains 30 seats. As you move to the rear of the auditorium, each row has 5 more seats than the previous row. \r<BR>\n" );
document.write( "\n" );
document.write( "How many seats are in the 13th row?       . \r<BR>\n" );
document.write( "\n" );
document.write( "How many seats are in the auditorium? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #599978 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=599978\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> This is an arithmetic series<BR>\n" );
document.write( "The first row has 30 seats, and the 13th row is 12 rows behind.\r<BR>\n" );
document.write( "\n" );
document.write( "N(13)=20+(13-1)*5<BR>\n" );
document.write( "N=20*60=80\r<BR>\n" );
document.write( "\n" );
document.write( "Sum=(1/2) {first row + last row}* n rows<BR>\n" );
document.write( "There are 20 rows, and by the above formula, row 20 has 20+(19*5)=115 seats.<BR>\n" );
document.write( "sum=(1/2)*20 (20+115)=1350 seats<BR>\n" );
document.write( "20+25+30+35+40+45+50+55+60+65+70+75+80+85+90+95+100+105+110+115 ;;; 20 rows\r<BR>\n" );
document.write( "\n" );
document.write( "adding the ones ending in 0, and get 650<BR>\n" );
document.write( "adding together the ones ending in 5=700<BR>\n" );
document.write( "sum is 1350 </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );