Hey shlok 

It is not possible to find marks from percentile score.

Because percentile is relative score in your shift .like if you score 80 percentile in a exam in which total students appear is 10000 than it means 2000 students score more marks than you.

Like in 100 marks exam if if 10 students appear and the marks are as follows: 10;20;30;32;34;35;37;38;45;50

Than student who score 50 got 100 percentile and student who score 30 got 30 percentile means 70% students score more than 30 marks.

Good luck