#17 - Global, Must Be True

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=17159)

The correct answer choice is (D)

As discussed during the setup, because at least two Ts must be selected, and W and Z cannot both be selected, we can deduce that either X or Y or both must be selected. Answer choice (D) is therefore correct.

[tld5061]

Is the fastest way to do this waiting until the end when you have the hypotheticals from other questions and eliminating choices and then trying your own hypotheticals? That was my approach but not sure if I missed an inference that could have made this easier. Mine were:
2S -> 1R, 3T (must have X, Y)
M->W not Z
M->W not H
T - must use 2 or 3

[tld5061]

Never mind I just answered my own question. Realize that you have to have X or Y or both since you must have at least 2 T and W & Z can't go together. MIssed that when I was trying to do it quickly!

[Stephanie Oswalt]

Never mind I just answered my own question. Realize that you have to have X or Y or both since you must have at least 2 T and W & Z can't go together. MIssed that when I was trying to do it quickly!

Glad you were able to figure it out tld! As always, let us know if you have any additional questions!

[lsat_novice]

I figured that answer D was the best answer, but I don't really understand why answer E is incorrect.

It looks like you always have to have 3 Topaze stones--either WXY or XYZ. That means that either X, or Z, or both is included in every selection.

What am I missing?

[lsat_novice]

Actually, is it possible to have 1 Sapphire, 3 Rubies, 2 Topazes?

In that case, I understand why E would be incorrect.

Is there a trick to thinking of all the number combinations quickly? I can tell that it's essential for figuring out the game but it takes me a lot of time to think through all the possibilities.

2 S + 1 R + 3 T
1 S + 2 R + 3 T (if WXY)
1 S + 3 R + 2 T
3 R + 3 T (if XYZ)
3 S + 3 T (if WXY)

[Adam Tyson]

Glad you figured out the problem with E! As to the numeric distributions, I find the best way is to think first about just the numbers and not worry about the categories. Those will come later in the process. So, what are the numeric possibilities?

3-3-0 (three from each of two categories, none from the third category)

3-2-1

2-2-2

We could also briefly consider a scenario with a group of 4, all the topazes, but since W and Z cannot be selected together we can quickly disregard those options (4-2-0 and 4-1-1).

From there, you can play around with which ones work and which ones do not. For example, the 2-2-2 scenario is impossible, because 2 from group S means just 1 from group R. That means you can only have either a 3-3-0 or a 3-2-1 scenario.

Once you have gotten to that point, you could try out a few templates based on those distributions, but that's probably not necessary here. Just keep those distributions in mind (and in your main diagram) for reference, and apply them as needed as you work through the questions. Here, for example, we can use the 3-3-0 to eliminate answer A, because 3 S and 3 T is possible (JKM and WXY).

Don't worry about getting all those combinations down up front. That sort of "Identify the Possibilities" approach is time consuming in the extreme and rarely an efficient, or necessary, approach.