Hi All,
It appears that all of the posters used Number Property rules to answer this question. You can also TEST VALUES; in that way, you can physically "see" how those same Number Property rules "work" in real life.
We're told that C and D are integers. We're asked if C is even. This is a YES/NO question.
Fact 1: (C)(D+1) is even
This means that one or the other (or both) of the "terms" must be even....
IF....
C = 2
D = 1
(2)(2) = 4
The answer to the question is YES
IF....
C = 1
D = 1
(1)(2) = 2
The answer to the question is NO
Fact 1 is INSUFFICIENT
Fact 2: (C+2)(D+4) = even
Just as in Fact 1, this means that one or the other (or both) of the "terms" must be even....
IF....
C = 2
D = 1
(4)(5) = 20
The answer to the question is YES
IF...
C = 1
D = 2
(3)(6) = 18
The answer to the question is NO
Fact 2 is INSUFFICIENT
Combined, we know....
(C)(D+1) is even
(C+2)(D+4) is even
Since D is an integer, ONLY ONE of the two terms - (D+1) and (D+4) - will be even; the other will be odd. As such, the other term in each of the products (the one with the C in it) MUST be even....
eg...
C = 2
D = 1
Combined, SUFFICIENT
Final Answer:
GMAT assassins aren't born, they're made,
Rich