If a^5b^3c^6 < 0, is abc < 0?

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This question is packed full of Number Properties, which you can use to answer the question.

We're told that (A^5)(B^3)(C^6) < 0. This tells us a few things:

1) NONE of the variables can equal 0 (since the product is LESS than 0)
2) C could be positive or negative.
3) Between A and B, one is positive while the other is negative.

The question asks if (A)(B)(C) is < 0. This is a YES/NO question.

Since we know that A and B will give us one positive and one negative, (A)(B) MUST be negative. Thus, the question 'hinges' on C....
IF....C = postive, then the product of (A)(B)(C) is negative and the answer to the question is YES.
IF....C = negative, then the product of (A)(B)(C) is positive and the answer to the question is NO.

Fact 1: B < 0

This tells us that A MUST be positive, but it tells us nothing about C.
Fact 1 is INSUFFICIENT

Fact 2: C > 0

This provides the essential piece of information that we need. We now know that the answer to the question is ALWAYS YES.
Fact 2 is SUFFICIENT.

Final Answer:

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

from stem
a and b has different signs and thus if c is +ve is the deciding factor whether abc<0

from 1

irrelevant

from 2

c is +Ve thus abc<0 ... suff

b