Hii,do not worry i will help you according to your query.Well,you can calculate you neet ug marks very easily.Just follow the steps:

There is an formula for calculating the percentile on the basis of an marks.

1st Method:

Invidual score x 100 divide by Marks obtained by the top Scorer 

2nd Method:

Formula calaculating the percentile on the basis of an rank

Total appearinbg candidate-Rank secured divide by Total appearing candidate x 100

Hope,this information will helpful for you.Goodluck.