To be honest you can't get B.Sc(Hons.) Mathematics with 83 percent in best 4 as last year the closing cutoff for B.Sc(Hons) Mathematics in Round 1 was around 93.75 and it was around 88 in Last Round, i.e Round 7.

Sometimes cutoffs changes but i don't think that it could change that much, a drastic change is not possible.

All the best!!