Why icai students need 50% overall to pass exam , can we filed rti ?

It is required to maintain the quality and demand for CA's. Believe it or no it is a good thing. 

In that case student who will secure more than 80% should have extra privelage rather than person who has 50% or less than 50%.

My Question is different - If any student is securing less than 50% in total but passed in all Individual subject should be consider as passed rather than Not Completed!

Our Invidividual Subject is so vast and very difficult to secure 50% to alll students who are working in Pvt. companies day /night and still behind this kind of courses.

"Our Invidividual Subject is so vast and very difficult to secure 50% to alll students who are working in Pvt. companies day /night and still behind this kind of courses" it is a personal choice. Further, have you seen the rankers who work day in and day out yet study whenever they can and sacrifice everything. 

You cannot have best of everything. So stop complaining about things that you cannot change and start doing something about the things that you can change.