Q21

[opulence2001]

Thanks so much! This game is very intimidating and the break down and diagram help a lot.

I understand why X must be followed by Z, but I'm not understanding why Z must only occur if preceded by X.

Why couldn't X be in year three, and Z in year two for example? I ask because for question 21 I narrowed down my options to B and C and choose C. I'm not seeing why W cannot precede Z and only X can. Could someone please explain further ?

[ManhattanPrepLSAT1]

The reason why W cannot precede Z for question 21 is that no matter what there must be exactly one X somewhere in year 1. That X must be followed by Z. Remember that nothing can follow an X other than Z.

If you have an X in year one followed by a Z in year two for some factory H, J or K, then you cannot also have a Z in either F or G in year 2. If there were that would mean that in year two there were two factories producing Z - violating the fourth constraint.

[m_elian]

At the beginning I couldn't understand why in question 21 choice C can't be correct.
It should look like that.
F--G
1 V W
2 W Z
3 / w

However when I looked deeply at the question I found out that if we applied choice C it will look like that:
F-G-H-I-K
1V W Z X (There r many possibilities but let's try this one)
2W Z x v ? (Here we have to X and V somewhere)
3

This means that in the second year factory K will have to make Z, because Z is only Car that can come after X. But we can't do that because Z can only be manufactured once a year. And Factory G already manufactured it.

In other words X has to be made in the first year and whoever will make it, will have to make Z in the second year and Z is already made by G in the second year.

It's tough one and I wonder who answered it only in one minute and 20 seconds.

[timmydoeslsat]

I agree that if you did not make the two inferences of:

X in a facility, that facility must do Z the next year

Z in a facility, that facility must do W the next year

...This game would take a little longer. However, those inferences just almost jump off the page at us! If V and W cant go in a facility the year after X was done...who is left to use? There are only 4 models. We also know that models cant repeat in the same facility in consecutive years.

And you can make the further inference that you know, in the first two years, that x cannot be the variable that repeats due to that producing multiple Z's in the following year.

In this local question, we are asked who could be assembled in factories F and G in the second year provided that in the first year F has V and G has W.

F G

V W

So we know that any answer choice that lists V on the left hand side or W on the right hand side would be incorrect due to elements repeating in consecutive years. Also any answer choice that contains 2 Z's, as we know only 1 Z can go per year.

This eliminates A, D, and E. I imagine most people are down to B and C to consider. And the only difference between these 2 answer choices is the factory of G. I know that X has not been placed yet. I know that when I do place X, and I will have to eventually because each model is done at least once per year, I know that a X will follow. So I know that there is no way I could waste a Z with it following the W in this case. If I had Z follow W in factory G for year 2, I would have to necessarily place 2 Zs in year 2 because once I place X in year 1, Z will follow in year 2 in that factory.

Answer B wins by process of elimination.