Question

A newly made car will have a model number, a parts number, and a serial number. A model number is assigned by the manufacturer to identify each type of car. A parts number identifies one part of the smaller parts that make up the car. A serial number is unique to each car produced and identifies it.

Which relation is a function?

(parts number, serial number)
(model number, parts number)
(serial number, model number)
(serial number, part number)

Answer 1

(parts number, serial number) --- no because every part number is related with many serial numbers

(model number, parts number) --- no because every model number is related with many parts number

(serial number, model number) --- yes because every serial number can have only one model number
(serial number, part number) --- no because a serial number is related with many part numbers