The relationship that is not functional is Situation 3: the total amount of money charged monthly on credit cards to the number of credit cards owned.
This is because one number of credit cards can correspond to multiple total amounts charged, depending on the spending habits associated with each card. For example, if a person has two credit cards, they could charge $500 on one and $200 on the other one month, amounting to $700 in total, or they could charge $300 on one and $100 on the other, amounting to $400 in total. Thus, the relationship does not provide a unique output (total amount charged) for each input (number of credit cards owned).
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