akpareek wrote:If ab = 1, what is the value of (axb)(ayb)?

1. ax = by = 2
2. 2xy = 4

Target question: What is the value of (axb)(ayb)?
This question is a great candidate for rephrasing the target question.
Aside: We have a free video with tips on rephrasing the target question: https://www.gmatprepnow.com/module/gmat- ... cy?id=1100

(axb)(ayb) = (ab)(ab)(xy)
= (1)(1)(xy) [since we're told that ab = 1]
= xy
Since (axb)(ayb) = xy, we can rephrase the target question. . .

Rephrased target question: What is the value of xy?

Statement 1: ax = by = 2
So, (ax)(by) = (2)(2)
Rearrange: (ab)(xy) = 4
Replace ab with 1 to get: xy = 4
Since we can answer the rephrased target question with certainty, statement 1 is SUFFICIENT

Statement 2: 2xy = 4
So, we can see that xy = 2
Since we can answer the rephrased target question with certainty, statement 2 is SUFFICIENT

Hmmm, there's a small problem with this question. On the GMAT, the statements are assumed to be true. Statement 1 essentially tells that xy = 4, BUT statement 2 tells that xy = 2. Are you sure you wrote the question correctly?

Answer = D

Cheers,
Brent