(3) Solution100+99-98-97+96+95-94-93+4+3-2.

=( 100+99-98-97)+(96+95-94-93)+....(4+3-2- 1)+ 1

=4+4+4+4+.....+ 1= 10 1

(4) Solution1999998+19998+19998+1998+88.

=2000000-2+200000-2+20000-2+2000-2+200-2+88

=2222200+78=2222278

(5) Solution (1+3+5+...+2001+2003)-(2+4+6+...+2000+2002)

=2003-2002+200 1-2000.....+3-2+ 1= 1+ 1+ 1....+= 1002

(6) Solution1+1/2+1/3+2/3+1/4+2/4+3/4+...+1/. kloc-0/+ 1/2+3/3+6/4+ 10/5+ 15/6+2 1/7+28/8+36/9+45/ 10=23.5

Sum of the nth item = 1+[(n- 1)n]/4

(7) Solution1.25× 67.875+125× 6.7875+1250× 0.053375 =125 x (0.67875+6.7875+0.