1/1*2+1/2*3+1/3*4+---1/1999*2000=?
问题描述：
1/1*2+1/2*3+1/3*4+---1/1999*2000=?
答
1/1*2+1/2*3+1/3*4+---1/1999*2000
=1-1/2+1/2-1/3+1/3-1/4+...+1/1999-1/2000
=1-1/2000
=1999/2000