#20 - Local, Must Be True

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=7326)

The correct answer choice is (E)

This is the most difficult question of the game. The question stem indicates that Z exports T and W, and as a consequence of the fourth rule, we can immediately infer that Y does not export T and W:

D04_Game_#4_#20_diagram 1.png

With nation Z’s exports fully assigned, crops O, R, and S must be exported by X and Y. Of course, from the second rule we know that when X or Y exports S, then the other must also export S, and we can then infer that S is exported by both:

D04_Game_#4_#20_diagram 2.png

O and R are the two remaining crops to be assigned. Because of the third rule, however, we can infer that R cannot be exported by Y because if R was exported by Y, we could not meet the condition of nations X and Z both exporting T. Thus, X must export R, and Y must export O:

D04_Game_#4_#20_diagram 3.png

This is the only solution to this question, and thus answer choice (E) is the correct answer.

The inference above that X and Y must export S is not easy to see, especially under the time pressure of the test. If you did not see the inferences above, you can still solve this problem effectively by using hypotheticals. The best approach for creating hypotheticals in this question would be to attack Y because we already have two Not Laws on Y. Because Y cannot export T or W, there are only three crops—O, R, and S—available for Y to export. Making hypotheticals that use two of these three crops for Y will quickly and effectively help you see why crop S must be exported by Y.


Answer choices (A), (B), (C), and (D): As shown in the diagram above, none of the statements in these answer choices can be true.

Answer choice (E): This is the correct answer choice.

[brcibake]

I thought B was the correct answer. Why is this incorrect? I do not understand what I am missing. How is it true that if Z exports tea and wheat, then y exports soybeans? This is because one of the crops has to repeat so this would force soybeans to repeat? I see how this answer could be true but not how it must be true. Thanks in advance!

[Jonathan Evans]

Hi, BRCI,

I made the following setup. Notice that if Z is exporting T and W, then since Y Z, Y is restricted to O, R, and S. Remember also that we need to assign two crops to X. Only one crop can be a double crop. If Y does not do S, then X must do S, but if X exports S if and only if Y does, so we have a contradiction. Therefore, Y must export S.

(Note that you may have approached this game with countries as groups instead of crops. That's probably an easier way to do this game, but either way works)