1/2×3+1/4×6+1/6×8+…+1/48×50

1/2×4+1/4×6+1/6×8+…+1/48×50=1/2[(1/2-1/4)+(1/4-1/6)+(1/6-1/8)+。。。+(1/48-1/50)]=1/2(1/2-1/50)=6/25