Suppose I need to model a bank which provides loans to different companies. Further suppose that the only companies in my data model are those to whom I am providing loans or have provided loans in the past.

What is the appropriate minimum cardinality for the relationship between LOAN and COMPANY?

Suppose I need to model a credit card company where each customer can receive up to one credit card and each card can be sent to only one address.

What is the appropriate maximum cardinality for the relationship between CUSTOMER and CARD?

Suppose I need to model a university where students can, but do not have to, participate in extra-curricular activities. Each such activity can have zero or more participants.

What is the appropriate minimum cardinality for the relationship between STUDENT and ACTIVITY?

Suppose I need to model a university where students can have up to three majors (i.e., can be part of three departments).

What is the appropriate maximum cardinality for the relationship between STUDENT and DEPARTMENT?

Suppose I need to model a hardware store with varying inventory. That is, not all products will be sold at any given time.

What is the appropriate minimum cardinality for the relationship between STORE and PRODUCT?