Similar to question pools, students receive a randomly selected subset of the questions included in a mastery set. This creates different versions of the assignment for each student. Students must answer a specified minimum number of these questions correctly to receive credit. The entire mastery set is graded as one question. Partial credit is not possible. The number of questions students are given and the minimum that they must answer correctly are set by you in the Assignment Editor.
Because the questions in a Mastery Set are graded as a single question, Mastery Set data is not available in Class Insights.
Example Mastery set in the Question Browser: 
Mastery set in an assignment: 
In this example, the mastery set includes 5 questions. It is set to display 3 of these questions to each student, and they must answer 2 of the questions correctly to earn credit.