#17 - Global, Must Be True

[Administrator]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=11371)

The correct answer choice is (C)

This is another “similarity of repair” question, and our diagram establishes that U and Y must share exactly one machine, namely T or V. Thus, answer choice (C) is correct.

Answer choice (A) can be a bit tricky, but, for example, U could repair T, and W could repair V, making answer choice (A) not necessarily true and thus incorrect.

Answer choice (B) is incorrect because U and X could repair two types of machines (R and T, or R and V).

Answer choice (D) is incorrect because W and Y could both repair T and V.

Answer choice (E) is incorrect because X and Y could both repair T and V.


One note of interest about this game is that all five of the questions are Global. This likely occurs because the rules contain so much information.

[Nicholas Noyes]

Hi,

I am confused as to why answer B could be incorrect. I thought that Urma and Xena both had to repair R at least. So would machine R count as "one type of machine" that Urma and Xena would both repair? I think I am getting thrown off by what the "exactly one type" means here. Also looking at this, I do not understand why answer choice D would be incorrect as well...since Wilm can repair T or V and Yolonda repairs both T and V wouldn't there be "exactly one type of machine" that both of them repair? Could you please clarify?

-Nick

[Adam Tyson]

Thanks for asking, Nick! "Exactly" means exactly that - no more, and no less. That's very different than "at least" or "at most," which allow for some flexibility.

U and X must have at least one machine type in common, as you pointed out, but they don't have to have "exactly" one because they could have two in common.

Likewise, while W and Y must have at least one machine in common (because W has to have at least one of the two that Y has), they don't have to have exactly one in common because they could have two in common (W could have both.)

Be exact in your thinking, and these numeric ideas will get easier to deal with! When you are told that a number is exact, it cannot change but must be that number and no other. When told "at least," that's a minimum requirement that allows for more, while "at most" is a maximum and could be less (including zero - if "at most four of my children are doctors," I might not have any children who are doctors.)

[lsat2022]

Is a good way of quickly answering this question to eliminate choices with unrestricted variables? So any answer choice with W or X could be eliminated immediately. Would this technique apply to just this question or can it be used in general?

Thank you!

[katehos]

Hi lsat2022!

I would caution against that approach as a means of eliminating answer choices. What if, for example, the correct answer choice said "there is exactly 1 type of machine that both Xena and Stacy repair"? This Must Be True, since Xena and Stacy must both repair a radio and Stacy cannot repair any other type of machine.

That said, I do think that can be a good strategy for prioritizing which answer choice you test first on a Must Be True question like this since we are looking for 100% certainty, which is much more easily accessible when variables are restricted. For example, you could use that strategy to focus your initial efforts on testing (C), which ends up being the correct answer! This way you can save some time and avoid accidentally eliminating a correct answer choice.

I hope that helps
Kate