Data Sufficiency

Gmat_mission wrote:Is x > y?

(1) 6x > 5y
(2) xy < 0

Target question: Is x > y?

Statement 1: 6x > 5y
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of x and y that satisfy statement 1. Here are two:
Case a: x = 1 and y = -1. Notice that 6x > 5y becomes 6 > -5, which is true. In this case, the answer to the target question is YES, x IS greater than y
Case b: x = 9 and y = 10. Notice that 6x > 5y becomes 54 > 50, which is true. In this case, the answer to the target question is NO, x is NOT greater than y
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: xy < 0
Let' s TEST some more numbers.
There are several values of x and y that satisfy statement 2. Here are two:
Case a: x = 1 and y = -1. In this case, the answer to the target question is YES, x IS greater than y
Case b: x = -1 and y = 1. In this case, the answer to the target question is NO, x is NOT greater than y
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 2 tells us that xy < 0 (i.e., xy is NEGATIVE)
If the product xy is NEGATIVE, then there are two possible cases:

Case a: x is POSITIVE and y is NEGATIVE .
Notice that this case ALSO satisfies statement 1, which says 6x > 5y. When we replace x and y, we get: 6(POSITIVE) > 5(NEGATIVE), which is always true.
In this case, the answer to the target question is YES, x IS greater than y

Case b: x is NEGATIVE and y is POSITIVE.
Notice that this case DOES NOT satisfy statement 1, which says 6x > 5y. When we replace x and y, we get: 6(NEGATIVE) > 5(POSITIVE), which is NEVER true.
So, it cannot be the case that x is NEGATIVE and y is POSITIVE.
In other words, only case a can be true, which means the answer to the target question must be YES, x IS greater than y
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent