1*1/4+4*1/7+7*1/10+...+97*1/100
=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)
=1/3*99/100
=33/100