Hello!!!
Delhi University takes admissions through merit based system and extrance exam system. However as far as your course is concerned i.e. BA (honours) in economics , you will get admission in all the colleges under DU except St.stephens( separate application is to be filled) though merit based system. In this system almost 11 cut off lists will be displayed based on best of four subjects of your 12th boards exam.
For further clarification please check the below mentioned link
https://www.google.com/amp/s/university.careers360.com/articles/du-admission/amp
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