Hello Dear,

Percentile score depends upon various factors so there is no any exact formula to get exact marks on 90 percentile it keeps changing. We can only tell you about the tentative score which can fetch you 90 percentile based on this assumption. Let me help you with an example for better understanding. If 100,000 students appeared for the examination and your percentile is 90, it means there are 10% of students ahead of you and 90% of students are behind you. You cannot predict your marks using your percentile but you can predict your rank. You can calculate your rank by using the below formula:
((100-percentile/100)*(total no of students)) +1 = your rank.

This is the tentative percentile depending upon previous years marks but it may change this year. So try to score minimum 10-15 marks more than the previous year score on same percentile.

180 marks=99.9+ percentile

150=99+ percentile

125=95+ percentile

100=88+ percentile

For more information you can visit the following link:

Good Luck