I first participated in round #604 solved 0 problem, then my rating was 1371 second #611 solved 1 problem, then my rating became 1248 third #649 solved 0 problem, then my rating became 1134 fourth #650 solved 1 problem, then my rating became 1036
even I solved atleast 1 problem in my fourth contest why my rating falled drastically..?
It depends on your rank in the contest, not the number of problems you solve.
cuz u enter more contest
your rating is converging to your real level, and (it seems that) your real level is much lower than 1500, so your rating falls rapidly