Building a Quiz

I am building a quiz which consist of 40 questions of which 20 will be available to learner.. All the questions are classified under 5 categories(eg: A,B,C,D,E) . I have used Question banks in my Quiz.. Now I am aware that I can randomize the questions in a question bank, but my requirement is to randomize the sequence of question appearing from the question bank. for example: the first question to appear from Category A, then the next should be from either B/C/D/E and so on. Also I require 4 question to appear from each category.

How can this be achieved?