Strong concept tested: Please help me out

[gmat620]

Is M < 0 ?

1. - M = | - M |
2. M^2 = 9

Hello Friends, I think mod is always positive, please help me out on this one...This question isn't tough but concept is required. I am little bit confused. Please help me. Thanks in advance.

[palvarez]

|a| = |-a|


1. -M = |M|, therefore M<=0. Insufficient, since M can be 0
2. M = 3 or -3. Insufficient.

Combined, M = -3. Sufficient.

C is the answer

[RoadtoIVY]

You are right mode is always positive:

Is M < 0 ?

1. - M = | - M |
2. M^2 = 9

1. - M = | - M | is true only for M=0, Hence M is not less than 0. Sufficient
2. M^2 = 9, gives you M=3,-3 hence Not Sufficient

IMO A

[gmat620]

OA C