There are two rating point for evry film,one u see and other u cant see(pehle imdb 250 walo ka sirf cant see wala dikhata tha).suppose there are two films a and b,both got 27k votes.Suppose from irregular a got 21k and 6k from regular voters.Suppose 21k ka 10/10 hota hai and baki 6k ka 7/10,and total u see is suppose 9/10..nw suppose b got 8.5 4m 21k irregular,8.3 from 6k regular,overall u see 8.4,then b will enter 250 coz it has 8.3 while a has 7.