Anita you have not mentioned which exam you are talking about. So I would not be able to help you exactly. Please mention the exam's name in the comments so that I would be able to assist you further.

Although if you are talking about 70 percentage, it is 0.7*total marks in the exam. If you are talking about 70 percentile, it is the marks you need to score to be in the top 30% of all students who appeared in the exam. It is subject to change every year based on the difficulty level of the question paper, number of students appeared and past year trends. Hope that helps.