Is ab < 0 ?

[VJesus12]

Is ab < 0 ?

(1) a = b - 6
(2) b < 0

The OA is the option C.

Why both statements together are sufficient? I couldn't determine the values of a and b.
Help, please.

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Hi VJesus12,

We're asked if (A)(B) is less than 0. This is a YES/NO question and can be solved by TESTing VALUES.

1) A = B - 6

IF....
A=0, and B=6, then (A)(B) = 0 and the answer to the question is NO.
A= -1, and B=5, then (A)(B) = -5 the answer to the question is YES.
Fact 1 is INSUFFICIENT

2) B < 0

IF...
A= -1, and B= -1, then (A)(B) = 1 and the answer to the question is NO.
A=1, and B= -1, then (A)(B) = -1 and the answer to the question is YES.
Fact 2 is INSUFFICIENT

Combined, we know...
A = B - 6
B < 0

Since we know that B is NEGATIVE, (B-6) will ALSO be negative - meaning that A will ALWAYS be NEGATIVE. When multiplying two negative numbers together, the product will ALWAYS be POSITIVE, so the answer to the question is ALWAYS NO.
Combined, SUFFICIENT

Final Answer: C

GMAT assassins aren't born, they're made,
Rich