i have given improvement in 2018 from bihar board and..i score 64 percent .I am in top 20 percentile is it is eligible to give jee main 2019
See you can give jee main 2019 and till then your result for the improvement exam will also be out so , it will be very easy for you. All the best!
If you score above 293 marks after improvements exam jnder General category then you shall stand eligible for Jee Mains for NIT, IIITs and GFTIs admission.
Cutoffs for all boards bekow.
https://engineering.careers360.com/articles/top-20-percentile-of-class-12-boards-for-nits-iiits-and-cftis/amp