Though the official cut offs haven't been released yet, 50 percentile is too less for qualifying in JEE Advanced. You will need atleast 85 percentile and above. You might have to attempt the 2nd JEE Mains session whenever it is held in 2020. Now cut offs change every year and are dependant on various factors like no.of Candidates who appeared for the exam, no.of Candidates who qualified, difficulty of the exam, Category and the no.of available seats. Please read our article for previous years cut offs of JEE Advanced: https://engineering.careers360.com/articles/jee-advanced-cutoff