Which table shows a proportional relationship between x and y?

A.
x y
2 9
4 18
6 27
8 36
10 45
B.
x y
2 2
4 8
6 18
8 32
10 50
C.
x y
1 4
2 7
3 10
4 13
5 16
D.
x y
1 5
2 6
3 7
4 8
5 9

1 answer

A proportional relationship means that the ratio \( \frac{y}{x} \) remains constant for all pairs of \( (x, y) \).

Let’s analyze each table:

Table A:

x  |   y
----------
2  |   9    →  \\(\frac{9}{2} = 4.5\\)
4  |   18   →  \\(\frac{18}{4} = 4.5\\)
6  |   27   →  \\(\frac{27}{6} = 4.5\\)
8  |   36   →  \\(\frac{36}{8} = 4.5\\)
10 |   45   →  \\(\frac{45}{10} = 4.5\\)

The ratios are all equal (\(4.5\)), so Table A shows a proportional relationship.

Table B:

x  |   y
----------
2  |   2    →  \\(\frac{2}{2} = 1\\)
4  |   8    →  \\(\frac{8}{4} = 2\\)
6  |   18   →  \\(\frac{18}{6} = 3\\)
8  |   32   →  \\(\frac{32}{8} = 4\\)
10 |   50   →  \\(\frac{50}{10} = 5\\)

The ratios are not equal, so Table B does not show a proportional relationship.

Table C:

x  |   y
----------
1  |   4    →  \\(\frac{4}{1} = 4\\)
2  |   7    →  \\(\frac{7}{2} = 3.5\\)
3  |   10   →  \\(\frac{10}{3} \approx 3.33\\)
4  |   13   →  \\(\frac{13}{4} = 3.25\\)
5  |   16   →  \\(\frac{16}{5} = 3.2\\)

The ratios are not equal, so Table C does not show a proportional relationship.

Table D:

x  |   y
----------
1  |   5    →  \\(\frac{5}{1} = 5\\)
2  |   6    →  \\(\frac{6}{2} = 3\\)
3  |   7    →  \\(\frac{7}{3} \approx 2.33\\)
4  |   8    →  \\(\frac{8}{4} = 2\\)
5  |   9    →  \\(\frac{9}{5} = 1.8\\)

The ratios are not equal, so Table D does not show a proportional relationship.

Conclusion: Only Table A shows a proportional relationship between \( x \) and \( y \).