IIT JAM 2018 Answer key https://scoop.eduncle.com/iit-jam-answer-keys has been released. If you solve previous papers then you must check the answer. It will help you to analyze your preparation.
When you prepared for IIT JAM Exam and complete your syllabus then you think your preparation is done but when you appeared in exam, you have a lot of anxiety about the result.
But, if you solve previous papers in advance then you have an idea about exam paper and after checking your answer you can focus on your weak areas.