It actually depends on the Scrum exam you are attempting. In case you have opted for the Certified Scrum Master (CSM) exam or Registered Scrum Master (RSM) exam, you should have attended a 2 days course and the exam should be relatively easy to clear. In case you have opted for the Professional Scrum Master I (PSM I) with or without course, a good preparation (2-3 weeks) based on the Scrum Guide is required as 80 questions need to be answered in 60 minutes (45 seconds per question).