#10 - Global, Must Be True

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=13934)

The correct answer choice is (E)

This type of question would normally be time consuming in the typical game. However, because we have all of the numerical information about the illnesses, and a significant amount of information about the symptoms of each illness, it is easier than would normally be expected. Some of the answers—such as (B)—can be eliminated with a quick glance at the original diagram.

However, there is a better way to think about this problem, and that is from an abstract standpoint. One way to force two illnesses to have exactly one symptom in common is to choose an illness with all three symptoms, and then pair it with and illness with exactly one symptom. This ensures that the two illnesses have exactly one symptom in common. Because M has all three symptoms, M must have at least one symptom in common with all other illnesses. Thus, it automatically has exactly one symptom in common with both K and N (although not necessarily the same symptom). M and K do not appear as one of the answer choices, but M and N do appear in answer choice (E). Because N only has one symptom it must be one of the symptoms that M has. Thus M and N have exactly one symptom in common and answer choice (E) is correct.

[saranash1]

The question states, "The illnesses in which of the following pairs must have exactly one symptom in common?

I understand how M & N works as the correct answer but couldn't J & L work as well since one of the rules states " Illnesses J & L have at least one symptom in common.

[Dave Killoran]

Hi Sara,

Thanks for the question. Take a close look at the wording in the question stem, and then at the words you used in suggesting J & L: the question stem says "must have exactly one symptom in common", whereas with J & L you say "at least." While J & L can have exactly one symptom in common, they can also have two symptoms in common, and thus J & L do not meet the stipulation of the question stem.

Please let me know if that helps. Thanks!

[kupwarriors9]

Hi can someone explain why C is correct and not E? Thank you.

Each of five illnesses–J, K, L, M, and N–is characterized by at least one of the following three...
The illnesses in which one of the following pairs must have exactly one symptom in common?

[Dave Killoran]

Hi can someone explain why C is correct and not E? Thank you.

Each of five illnesses–J, K, L, M, and N–is characterized by at least one of the following three...
The illnesses in which one of the following pairs must have exactly one symptom in common?

The explanation for #10 is a separate post, over here: viewtopic.php?f=441&t=4079 [Admin note: this post was originally on the setup page, it has now been moved to the thread discussing #10]

When we do LG explanations, the setup gets its own, and then each question gets its own post

Please review the explanation above, and let us know if you have any additional questions!

[kupwarriors9]

Thanks so much!!! I was wondering if you saw the other posts I made a few days ago. Thank you so much Dave!!! You're the best

Hi can someone explain why C is correct and not E? Thank you.

Each of five illnesses–J, K, L, M, and N–is characterized by at least one of the following three...
The illnesses in which one of the following pairs must have exactly one symptom in common?

The explanation for #10 is a separate post, over here: viewtopic.php?f=441&t=4079 [Admin note: this post was originally on the setup page, it has now been moved to the thread discussing #10]

When we do LG explanations, the setup gets its own, and then each question gets its own post

Please review the explanation above, and let us know if you have any additional questions!

[mollylynch]

How do we know N only has one symptom? Something to do with L?

[Adam Tyson]

It is indeed about L, Molly, and about the numeric restrictions in the game.

L must have more than K, so L must have at least 2. But L and N have nothing in common, so L cannot have all 3, as that would leave N with none. Thus, L must have 2 of the symptoms and N must have only the third symptom.