1/1*4+1/4*7+1/7*10+10*13+.+1/94*97+1/97*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