Final answer:
Set A, described using the roster method, contains the even numbers between 5 and 10, which are 6 and 8. The set has a cardinality of 2 and is well-defined as it clearly states the property for membership.
Step-by-step explanation:
The method used to describe set A, which is {even numbers between 5 and 10}, is known as the roster or tabular method. It explicitly lists the elements that are in the set by property. The elements of set A are the even numbers that fall between 5 and 10, which are 6 and 8. Therefore, set A is written as {6, 8}. The cardinality of set A, which is the number of elements in the set, is 2. A set is considered well-defined if its definition specifies a clear rule for deciding whether a given item is a member of the set. In this case, set A is well-defined because the rule 'even numbers between 5 and 10' is clear and unambiguous, and there can be no dispute about which numbers belong to the set.