奥数题6年级1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+...1/39*40

1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+。。。1/39*40=1-1/2+1/2-1/3+。。。+1/39-1/40=1-1/40=39/40