Data Sufficiency

[GMAT math practice question]

m and n are integers. Is m + n an odd number?

1) m - n = 2
2) m^2n^2 = 225

=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

Condition 2)
Since m^2n^2 = 225 is an odd number, both m and n must be odd numbers, and m + n is an even number.
Thus, the answer is 'no', and condition 2) is sufficient by CMT (Common Mistake Type) 1.

Condition 1)
Since m - n = 2, both m and n are odd numbers or even numbers.
Since m and n have the same parity, m + n is an even number.
Thus, the answer is 'no', and condition 1) is sufficient by CMT (Common Mistake Type) 1.

Therefore, D is the answer.
Answer: D