Which set of ordered pairs is not a functions? A. (3,1), (2,1), (1,2), (3,2)
B. (0,0), (1,1), (2,2), (3,3)
C. (4,1), (5,1), (6,1), (7,1)
D. (1,2), (3,4), (4,5), (5,6)

A

Step-by-step explanation:

X values cannot repeat in a function, 3 is used as an X value twice in A, and therefore cannot be a function.

If this is graphed, you can use the vertical line test, if a vertical line on any point goes through other points, it is not a function.

In this case, just check if X repeats.

this is a direct variation proportion. y = kx

y is the total amount due, k is the constant of variation, and x is the number of texts sent.

plug in the 3.20 and the 16 to solve for the "k". this is the constant of proportionality. it is the value that will not change.

3.20 = k(16). solving you get $.20 per text.

the equation would then be y = .20x