Which of the tables represents a function?

Table A
Input Output
7 2
8 1
5 6

Table B
Input Output
5 2
3 5
5 6

Table C
Input Output
1 2
1 9
7 3

Table D
Input Output
2 6
6 7
6 2

Question

Which of the tables represents a function?
 

Table A
Input	Output
7	           2
8	           1
5	           6

Table B
Input	Output
5	           2
3	           5
5	           6

Table C
Input	Output
1	            2
1	            9
7                  3 

Table D
Input	Output
2	            6
6	            7
6	            2

mathstudent55 · Answer

In order to be a function, the input can have each different number only once.

mathstudent55 · Answer

If you see any number used more than once in the input, it is not a function.