## Practice questions

- Is the relation {(2, 5), (3, 7), (4, 1), (8, 1)} a function?
**A.**The relation is a function because no element of the range is paired with more than one element of the domain.**B.**The relation is a function because no element of the domain is paired with more than one element of the range.**C.**The relation is NOT a function because 1 is paired with both 4 and 8.**D.**The relation is NOT a function because no element of the domain is paired with more than one element of the range.**E.**The relation is NOT a function because 2 is paired only with 5. - Does the following mapping represent a function?
**A.**It does represent a function because each number in the domain is paired with at least one number in the range.**B.**It does represent a function because each number in the range is paired with at least one number in the domain.**C.**It does NOT represent a function because 2 is paired with both 1 and 12.**D.**It does NOT represent a function because 5 is paired with both 7 and 10.**E.**It does represent a function because no number is listed more than once in the left column.

## Answers and explanations

- The correct answer is Choice
**(B).**None of the domain numbers (first numbers in the ordered pairs) are paired with more than one range element. In other words, no first number is repeated with a different second number, so the relation is a function. - The correct answer is Choice
**(D).**The domain element 5 is paired with 7 and 10. It's therefore paired with more than one range element, so it isn't a function. Choices (A), (B), and (E) are incorrect because they have the wrong conclusion and false definitions of*function.*Choice (C) has the right conclusion but a false definition.