Hello

It would be difficult to calculate the marks using the percentile score. Calculation of the exact rank is also tough. However, we can calculate the probable rank using the formula mentioned below-

100 - your total percentile score is the percentage  of people ahead of you. 869010 are the number of candidates appeared for Jan exam. So rank formula is (100 - your total score) X 869010 /100. If the number of candidates for April exam increased to 1200000 then your final rank shall be (100 - your total score) X 1200000/100

With 75 percentile score, your probable rank would be around 217252.

Good Luck!