Data Sufficiency

Nina1987 wrote:If (x+y)/z = -2, is x positive?

(1) z is negative.
(2) y is positive.

Target question: Is x positive?

Given: (x + y)/z = -2
Since the question asks about the variable x, let's solve this equation for x.
(x + y)/z = -2
So, x + y = -2z
And, x = -2z - y

This allows us to REPHRASE the target question....
REPHRASED target question: Is -2z - y positive?

Aside: We have a free video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

Statement 1: z is negative
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of z that satisfy statement 1. Here are two:
Case a: z = -1 and y = 1. In this case -2z - y = -2(-1) - 1 = 1 = a POSITIVE NUMBER
Case b: z = -1 and y = 3. In this case -2z - y = -2(-1) - 3 = -1 = a NEGATIVE NUMBER
Since we cannot answer the REPHRASED target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: https://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: y is positive
This statement doesn't FEEL sufficient either, so I'll TEST some values.
There are several values of y that satisfy statement 2. Here are two:
Case a: z = -1 and y = 1. In this case -2z - y = -2(-1) - 1 = 1 = a POSITIVE NUMBER
Case b: z = -1 and y = 3. In this case -2z - y = -2(-1) - 3 = -1 = a NEGATIVE NUMBER
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
There are several values of y and z that satisfy BOTH statements. Here are two:
Case a: z = -1 and y = 1. In this case -2z - y = -2(-1) - 1 = 1 = a POSITIVE NUMBER
Case b: z = -1 and y = 3. In this case -2z - y = -2(-1) - 3 = -1 = a NEGATIVE NUMBER
Since we cannot answer the REPHRASED target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

Cheers,
Brent

Nina1987 wrote: what should be the difficulty level of this problem?

I'd say it's a 500-level question.

Cheers,
Brent