1/1*2+1/2*3+1/3*4+.+1/2004*2005
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+……+(1/2004-1/2005)
=1-1/2+1/2-1/3+1/3-……+1/2004-1/2005
=1-1/2005
=2004/2005
1/1*2+1/2*3+1/3*4+.+1/2004*2005
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+……+(1/2004-1/2005)
=1-1/2+1/2-1/3+1/3-……+1/2004-1/2005
=1-1/2005
=2004/2005