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Re: DS: From GMATPREP [#permalink]
12 Feb 2009, 09:02

OA is C. I am not familiar with this picture method. I ended up doing addition of inequalities and got the answer on the test and I probably spent 2-3 min on this question.

(1) m - 3z > 0. Insufficient on its own. (2) 4z - m > 0. Insufficient on its own.

(1)+(2) Remember we can add inequalities with the sign in the same direction --> m-3z+4z-m>0 --> z>0, so z is positive. From (1) m>3z=positive, so m is positive too (m is more than some positive number 3z, so it's positive) --> m+z=positive+positive>0. Sufficient.