(1+3+5+ ``` ＋1999+2000+2001)-(2+4+6+```+1998+2002）
=(1-2)+(3-4)+(5-6)+```+(2001-2002)
=-1*2002/2
=-1001
99`````````9 Ⅹ 99`````````9+1999```````9
（2000個9） （2000個9） （2000個9）
=(10`````````0-1) Ⅹ 99`````````9+1999```````9
（2000個0） （2000個9） （2000個9）
=99`````````900`````````0-
(2000個9) (2000個0)
99`````````9+199`````````9
(2000個9) (2000個9)
=99`````````900`````````0+100`````````0
(2000個9) (2000個0) (2000個0)
=10000``````````````````00
(4000個0)