Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Is M<0?

(1) -M = |-M|

(2) M^2 = 9

In the original condition, there is 1 variable(m), which should match with the number equation. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer. For 1), in order to make -m=|-m|, from -m>=0, m<=0, m=-1 -> yes, m=0 -> no, which is not sufficient. For 2), m=-3 -> yes, m=3 -> no, which is not sufficient. In 1) & 2), m=-3 is yes and sufficient. Therefore, the answer is C.

-> 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.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare

The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.

Find a 10% off coupon code for GMAT Club members.

“Receive 5 Math Questions & Solutions Daily”

Unlimited Access to over 120 free video lessons - try it yourself

See our Youtube demo