Hello.
you got 78 percentile in JEE mains now it is quite difficult to predict your exact rank but you can calculate your approximate rank by using the below formula:
((100- your percentile score) X 869010/100)
Let's suppose in April exam the number of candidates appeared will increase to 12,00000 then you can calculate your approximate rank by the given formula:
((100-your percentile score) X 12,00000/100)
Now using the above formula your approximate rank would be: 191,182 remember this rank is considered as general category rank.
Now for predicting colleges on the basis of your percentile score you can use our college predictor tool from the below link:

Best of luck.

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