You can easily move or copy individual questions from one Question Bank to another.
In the Course Navigation, click the Quizzes link.
Click Manage Question Banks
Click the Settings icon  and click the Manage Question Banks link .
Open Question Bank
Open the Question Bank by clicking the title of the Question Bank.
Move/Copy Questions to Another Bank
Click the move/copy question to another bank link to move/copy the question to another question bank.
Select Question Bank
Click the title of the bank  where you would like to copy/move the questions. Click the Keep a copy in this question bank as well checkbox  if you only want to copy the question. Then click the Move/Copy Questions button  to copy the question.
View Moved/Copied Question
View the moved/copied question in the new bank.
Note: Changes to questions won't automatically update quizzes that are already using those questions unless you remove the question and re-add it.