The study guide indicates that approximately 13% of the weighting for the Salesforce Admin 201 certification is given to the topic of Analytics, Reporting and Dashboards.
Given that there are 60 questions, you could expect around 8 questions. This is one of the main topics in the administrator certfication, so you must know it well.
Here is an example of a Matrix report. It has been setup to show lead sources by month. Note that it also includes the sum of expected revenue.
Salesforce Joined Reports
Here is an example and description of what a joined report is and how it can be used, using the example of opportunities.