Playing with formal logic about 4 minutes, I think that the answer is A.
Hey, Stolyar! See how handy that formal logic crap is? Do you think you could have solved this without it?
(Note: i posted a formal logic drill about a week ago and only Stolyar attempted to solve it. Seems it may have done some good! <grin>).
This is pretty straightforward if you can quickly "interpret" the premises in the statement in simple "if then" form. As far as "formal logic" goes, there is only one rule you need to know: "if P then Q" is equivalent to "if not Q then not P". The solution looks long and complicated only because I am writing EVERYTHING out in detail. (I would normally make concise diagrams with symbols).
1) Unless negotions begin soon, the cease-fire will be violated by one of the two sides to the dispute.
2) Negotiations will be held only if other countries have pressured the two sides to negotiate;
3) an argeement will emerge only if other countries continue such pressure throughout the negotions.
4) But no negotiations will be held until international troops enforcing the cease-fire have demonstrated their ability to counter any agression from either side, thus suppressing a major incentive for the two sides to resume fighting.
Here are the "logical" translations of all of the premises into basic "if-then" form:
1: If negotiations do not begin soon, the cease-fire will be violated
If the cease-fire is not violated, then the negotiation must have been held soon
2: If negotiations are held, then other countries must have applied pressure.
If the other countries do not apply pressure, then the negotiation will not be held.
3: If aggreement emerges, then other countries must have sustained pressure.
If countries do not sustain pressure, then an aggreement will not emerge.
4: If international troops do not enforce the treaty, then negotiations will not be held.
If negotiations are being held, then it must be true that international troops have demonstrated there ability to counter aggression thus suppressing a major incentive to resume fighting.
If the above is true AND given that:
"negotions between the two sides do begin soon, at the time home negotiations begin" which means
"The negotiation were begun soon and are now proceeding."
Which of the following is NOT a logical conclusion of the above? (I.e., "Which of the following is either NOT true, or NOT NECESSARILY true?" or "All of the following MUST BE TRUE except which answer choice?")
A) The cease-fire has not been violated by either of the two sides
(1) says "If negotiation do not begin soon then cease fire violated". Although we are given that negotiations did begin soon, we cannot concllude that the cease fire was violated.
(Given "if P then Q" and "P is not true", we cannot conclude anything about Q). Assuming "Q is not true" based on "P is not true" is such a common error that it has its own name: it is called the "denying the premise" fallacy) . Hence, A is not necessarily true and we can stop right here.
Let's examine the other four choices:
B) International troops enforcing the cease-fire have demonstrated that they can counter aggression from either of the two sides.
According to (4), if negotiations are held, then the international troops must have demonstrated their ability . . . . Since negotiations have indeed started. (B) MUST be true.
C) A major incentive for the two sides to resume hostilities has been suppressed.
(C) is a direct consequence of (B). Since B must be true, C also must be true.
D) Other countries have exerted pressure on the two sides to the dispute. - Is this a typo? What the hell does LSAT mean here?
According to (2), if negotiations are held, then pressure must have been applied by other countries. Since negotiations are being held, (D) MUST be true.
E) The negotiations' reaching an agreement depends in part on the actions of other countries.
According to (3), if an agreement emerges, then other countries must have continued to applied pressure. Equivalently, If other country do not apply pressure, an agreement will NOT be reached. Since the emergence (or lack of) an agreement is clearly dependent on whether other countries apply pressure or not, this constitutes a dependence on the actions of other countries. Hence, (E) must be true.
Hence, A is the only choice that is NOT NECESSARILY TRUE and thereby the correct answer choice.
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993