If x is an integer, is 3x odd?
(1) x + 2 is an even integer.
(2) y is an even integer such that 24/y=x
If we modify the original condition and the question, we can modify the question from 3x=odd? to x=odd? There is 1 variable (x) in the original condition. In order to match the number of variables to the number of equations, we need 1 more equation. Since the condition 1) and the condition 2) each has 1 equation, there is high chance that D is the correct answer.
In case of the condition 1), from x+2=even, we get x=even-2=even. The answer is no and the condition is sufficient.
In case of the condition 2), if y-2 we get 24/2=12=x=even, which is no. However, when y=8, we get 24/8=3=x=odd, which is yes. Therefore, the condition is not sufficient.
The correct answer, thus, is A.
l For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.