(1/2*4)+(1/4*6)+(1/6*8)+……+(1/48*50)=(1/2)*{【(1/2)-(1/4)】+【(1/4)-(1/6)】+……+【(1/48)-(1/50)】}=(1/2)*【(1/2)-(1/4)+(1/4)-(1/6)+……+(1/48)-(1/50)】=(1/2)*【(1/2)-(1/50)】、=(1/2)*(12/25)=6/25