Bunuel
Is \(x > y\) ?
(1) \((x – y)^3 > (x – y)^2\)
(2) \((x – y)^4 > (x – y)^3\)
Target question: Is \(x > y\) Statement 1: \((x – y)^3 > (x – y)^2\) From this information, we can conclude that (x - y) does not equal zero
This means that (x - y)² must be POSITIVE, which means we can safely take \((x – y)^3 > (x – y)^2\) and divide both sides by (x - y)²
When we do so, we get: x - y > 1
If x - y > 1, we can also conclude that x - y > 1 > 0
If x - y > 0, we can add y to both sides to get
x > yThe answer to the target question is
YES, it's the case that x > ySince we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: \((x – y)^4 > (x – y)^3\)In this case it might be tempting to use the same strategy we used for statement 1 and divide both sides of the inequality by (x - y)³
The problem with this approach is that we don't know whether (x - y)³ is positive or negative.
Consider these two conflicting cases (both of which satisfy statement 2):
Case a: x = 2 and y = 0. In this case, the answer to the target question is
YES, it's true that x > yCase b: x = 0 and y = 2. In this case, the answer to the target question is
NO, it's not the case that x > ySince we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent
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