You choose the number of questions to randomly use from that category.
If a question from that category is already in use, it will NOT be selected again as one of the random questions.
If the category has questions you DO NOT want to be part of the random draw process, you need move and save them all in a new category.
Only top level categories and their questions will be accessible from the Edit Quiz page.
Selecting random questions from a question bank category
Go to the course homepage and click the quiz.
In the Administration block on the left, under the Quiz Administration heading, click Edit quiz.
To add random questions to a specific quiz page:
Scroll to the desired page.
Click Add after the last question on the page, then select a random question from the menu.
Select a Category from the menu from which to pull the random questions from.
Decide whether to include subcategories.
Set the number of random questions to pull.
Click Add random question. The new Random question will be added to the page, listing the source category.
The Edit quiz page will now display another question on the page. The question will have a dice icon next to it and give the name of the question category that a random question will be pulled from for that question.