=1/1*4+1/4*7+1/7*10+……+1/97*100=(1/3)*(1-1/4)+(1/3)*(1/4-1/7)+(1/3)*(1/7-1/10)+……+(1/3)*(1/97-1/100)=(1/3)*(1-1/4+1/4-1/7+1/7-1/10+……+1/97-1/100)=(1/3)*(1-1/100)=33/100