Dear candidate

If you are talking specially about university of Delhi's calculation of top 4 subject,then you are right only top 4 %  is calculated for cut off to get admission in colleges.but in other colleges of country this method of calculation is not applicable all over india.generally colleges takes admission directly on the basis of your actual % of marks obtained at 12 th level.

Hope this will helpful.thanks

Usually best of 5 is taken in Science out of which PCB/PCM and English are compulsory. In arts most colleges like DU consider the best of 4 for admissions. According to CBSE, your percentage calculation is done on the basis of best of 5 subjects. So it depends on which college you want to go for and which stream you belong to.