CAT percentile is calculated using the formula: P=(R*N)/100, where P is percentile, R is Rank of the Candidate based on the CAT score and N is the no.of Candidates who appeared for the exam. Every correct answer gives you 3 marks and so assuming you write 5 correct answers, your score will be 15. Now we will need to calculate your rank and for that we will need the no.of Candidates who appeared for the exam and the Candidates who have scored lesser than you. Now there is sectional percentile as well. So assuming you scored 1 correct answer in each section and scored 2 in QA, your percentile would be roughly 4-5. This is just an assumption because we do not know how many would appear for the exam and how many would score lesser than you.