简便运算1990/1990*1991+1990/1991*1992+......+1990/2001*2002=

（1/1990*1991+1/1991*1992+......+1/2001*2002）×1990 =（1/1990-1/1991+1/1991-1/1992+......+1/2001-1/2002）×1990 =1-1990/2002=1-995/1001=6/1001 满意请采纳