How much helpful are the previous year question papers for any examination?
Previous year question papers are very helpful. The previous year question papers helps in understanding the paper pattern, type of questions, marking scheme, difficulty level, and even changing trends . At times, questions are even repeated in the exam. Moreover, the previous years board exam papers are always considered as a sure shot way of covering a good part of syllabus effectively in a relatively less time.
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Since you haven't mentioned the name of any examination, I'm giving you a general answer. To be honest the previous year question papers are really very helpful. It gives you an idea of the trending questions. You can even get some common questions if you solve the last 10 to 15 years question papers. In case of JEE Main and NEET, you can get a large number of questions from the previous year papers. So you should obviously solve those papers atleast twice. Also solve mock tests regularly. If you follow these steps, you can definitely get good marks in any examination.
Hope this information helps you.