I am 12 pass out and not joined any couching institute and i am preparing for BITSAT,VITEEE How can i do it by sitting at home?
The first thing you should do is check the syllabus for both the exams and then brush up all these concepts. Practice as many questions as you can and keep it time bound to improve speed. You can answer previous year papers or sample papers to give you an idea of the kind of questions that will be asked.
All the best!