Determine if the relation of ordered pairs are functions

Question

Input, Output

15,0

10,5

5,10

10,15

15,20

 

In looking at these pairs, I would guess that since each has a least one output, that would indicate a function.  However in the first pair, an input of 15 results in 0.  After that pair, for every <5> in input, the output +5.

Answer 1

A function is single value.  Each input can only have 1 output.  This is not a function because the input value of 15 has 2 output values(0 and 20).  Same thing with input value 10, it has 2 output values(5 and 15), so this is not a function.