Ratio question PS

[Strongt]

18. w, x, y, and z are all positive integers. Which of the following proportions is NOT equivalent to the others?

a. y/w = z/x
b. z/y = x/w
c. w/y=x/z
d. w/z = x/y
e. x/w = z/y

i tried plugin' in numbers but didnt manage to get the answer...

answer is D

[Ian Stewart]

18. w, x, y, and z are all positive integers. Which of the following proportions is NOT equivalent to the others?

a. y/w = z/x
b. z/y = x/w
c. w/y=x/z
d. w/z = x/y
e. x/w = z/y

i tried plugin' in numbers but didnt manage to get the answer...

answer is D

Plugging in numbers seems to me to be a time-consuming way to answer the question. If, looking at answer A, y/w = z/x, then cross-multiplying we have yx = wz. You can do the same for every answer choice, and, with the exception of answer D, each gives the equation yx = wz. So D is not equivalent to the rest.

[GMATGuruNY]

18. w, x, y, and z are all positive integers. Which of the following proportions is NOT equivalent to the others?

a. y/w = z/x
b. z/y = x/w
c. w/y=x/z
d. w/z = x/y
e. x/w = z/y

i tried plugin' in numbers but didnt manage to get the answer...

answer is D

Perhaps you made an arithmetic error.

Let's plug in values that satisfy answer choice A.

A: y/w = z/x.
Let y=4, w=2, z=6, x=3.
4/2 = 6/3. This works.

Now let's plug these values into the remaining answer choices:

B: z/y = x/w.
6/4 = 3/2. This works.

C: w/y=x/z.
2/4 = 3/6. This works.

D: w/z = x/y.
2/6 = 3/4. Doesn't work.

The correct answer is D.

For the skeptical, here's E:

E: x/w = z/y.
3/2 = 6/4. This works.

Cross-multiplying all the answer choices (as suggested by Ian) seems easier. But plugging in values is a perfectly valid approach.