Question

1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 -..+ 2006

Answer 1

=(1+2-3-4)+(5+6-7-8)+...+(2001+2002-2003-2004)+2005+2006

=-4+(-4)+(-4)+...+(-4)+2005+2006

=501(-4) +2005+2006

=-2004 +2005+2006

=2007

Answer 2

   1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - ... + 2006

= 1 + ( 2 - 3 - 4 + 5 ) + ( 6 - 7 - 8 + 9 ) + ( 10 - 11 - 12 + 13 ) + ... + ( 2002 - 2003 - 2004 + 2005 ) + 2006

= 1 + 0 + 0 + 0 + ... + 0 + 2006

= 1 + 2006

= 2007

                           chuk hok tốt