Q22

[matthew.beaudoin]

can someone help me out with this one? What's the best way to work through it?

[noah]

Let me explain this "real time."

Since this is a conditional question, our first job is to see what we can infer from the new condition. If G is 5th, then we know what?

We know that K is sixth. What else? If you're stuck, think "who's left?" We know that we have to place L - F before the G, and we still have the M - J and the H/M _ _ + H/M chunk. There's a lot left to place. We know we'll definitely have L - F and M before G, so next let's think about the chunk. Where could it go? We could place H first and M fourth, but that forces L into 2nd, so that doesn't work, so it must be that M comes before H. Can we place M first and H fourth? No, because that again forces L into 2nd. So, what about M first and H 7th? That seems to work.

Since we're looking for a must be true, I shouldn't be happy with having simply come up with any old scenario. Does M have to be first? No, it could be 4th and M 7th.

At this point, I probably would see if M always has to be 7th by trying to place it somewhere else. It can't go anywhere else, so (B) is our answer.

Alternately (and less ideally), once I know that M could go first I'd come up with a working scenario (M J L F G K H) and see who I can eliminate - since it's a must be true question, anything that doesn't come up in a valid hypothetical isn't the answer. This hypothetical allows me to eliminate (A), (C), (D) and (E). So, that would have done it also! Note that it doesn't always work out so nicely, but in a pinch, that's a great strategy to pull out.

Tell me if you have any questions.

[matthew.beaudoin]

Thanks for the explanation, Noah. It was very helpful. I was having a lot of trouble keeping track of the H and M chunk/relationship. I need to keep working at this one!

[KARLA.SAAVEDRAB]

Hello,

My question would be, how do we know that M has to go before G? Could it not be LHFMGKJ?

Thank you!

Let me explain this "real time."

Since this is a conditional question, our first job is to see what we can infer from the new condition. If G is 5th, then we know what?

We know that K is sixth. What else? If you're stuck, think "who's left?" We know that we have to place L - F before the G, and we still have the M - J and the H/M _ _ + H/M chunk. There's a lot left to place. We know we'll definitely have L - F and M before G, so next let's think about the chunk. Where could it go? We could place H first and M fourth, but that forces L into 2nd, so that doesn't work, so it must be that M comes before H. Can we place M first and H fourth? No, because that again forces L into 2nd. So, what about M first and H 7th? That seems to work.

Since we're looking for a must be true, I shouldn't be happy with having simply come up with any old scenario. Does M have to be first? No, it could be 4th and M 7th.

At this point, I probably would see if M always has to be 7th by trying to place it somewhere else. It can't go anywhere else, so (B) is our answer.

Alternately (and less ideally), once I know that M could go first I'd come up with a working scenario (M J L F G K H) and see who I can eliminate - since it's a must be true question, anything that doesn't come up in a valid hypothetical isn't the answer. This hypothetical allows me to eliminate (A), (C), (D) and (E). So, that would have done it also! Note that it doesn't always work out so nicely, but in a pinch, that's a great strategy to pull out.

Tell me if you have any questions.

[e.sterlingsmith]

Hello,

My question would be, how do we know that M has to go before G? Could it not be LHFMGKJ?

Thank you!

In your scenario M is before G, but I believe you meant how do we know it has to go after? It cannot be before G because of the at least two sessions between H and M rule. In your hypothetical there is only one (F).

[ElizabethM261]

Hello,

I see how you could there with process of elimination, however I actually chose D because the first set I did was "LMJFGKH." I understand now that D could be true doesn't have to be true, so I should have kept going with the diagramming.

My is question is with these types of questions, how do we know which ones will be process of elimination versus which ones can be done with a simpler strategy? I know some questions, you just "see" the right answer, pick it and move on.

Thanks!
Liz

[ohthatpatrick]

Hey, Liz.

For most questions in Games there is both a "clever" way to do it and a "brute force" way to do it.

If you know the "clever" way, take it! If you just "see" the answer, pick it!

If you don't, get going on "brute force". My success on this section of the test has almost always been "brute force". As soon as I'm not sure of what to do or what to think, I just start writing hypotheticals, and those give me all the ammunition I need to get all the answers right.

So I would recommend that you embrace the challenge of getting faster/smoother with brute force, because he's the type of friend that doesn't betray you when the stress of a real test makes it harder to be 'clever'.

In terms of the problem with how you approached Q22, it seems like you don't know the fundamental difference between the two types of ideas.

1. COULD BE TRUE / MUST BE FALSE = possible vs. impossible
To check whether an answer is possible, we try to write a scenario that matches the answer.

2. MUST BE TRUE / COULD BE FALSE (rare) = unavoidable vs. avoidable
To check whether an answer is avoidable, we try to write a scenario that DOESN'T match the answer.

Your first possible scenario was LMJFGKH

Eliminate (A), because having F on 3 is avoidable.
Eliminate (C), because having J on 4 is avoidable.

We can't use LMJFGKH to eliminate B/D/E, because those three answers match our scenario. Our scenario shows that B/D/E are possible. We only can assess whether they're mandatory or avoidable by trying to find counterexamples.

by the way, why would you pick (D), if your scenario also matched (B) and (A)?

L - F - GK
M - J

If we're analyzing (B), we're thinking, "Does H have to be last? Could someone else go last?"

GK are locked into 5 and 6.
__ __ __ __ G K __

We know we have L - F - GK,
so the only leftover pieces are M, J, and H.

Since we have M - J rule, we can't put M last. Thus, the only person besides H that could be last would be J.

__ __ __ __ G K J

This would force M/H __ __ H/M to be split up onto 1 and 4.
M/H, __ , __ , H/M, G, K, J

When you try to insert L - F - GK, you have to put L into 2 and F into 3.
M/H, L , F , H/M, G, K, J

But that breaks the rule that L can't be in 2. So by trying to find a counterexample to (B), we found out there ARE no counterexamples, which tells us that this answer must be true.

It's often hard at that final moment on Must Be True brute forcing: "This counterexample scenario I just tried blew up --- so, that means the answer is correct?"

Yes!

If you feel uncomfortable with that process, then you can defer on (B) when it seems like a counterexample ain't happening, and move onto (D) or (E) with that scenario you had:
LMJFGKH

For (D), can we move anyone else to spot 1? Sure, we could do
M J L F G K H

That eliminates (D) and, as it happens, also lets us eliminate (E).

Hope this helps.

[VendelaG465]

Hi Pat quick question i was a bit confused reading this part of your explanation for #22
" No, because M - J. Okay, then can we put J last?
L H F G K M J

Sure!

We can eliminate (B), because having H on 7 is avoidable.
And as an unexpected bonus, we can eliminate (E) because having M on 2 is avoidable.

I'm confused with this scenario "LHFGKMJ" I thought the given condition was G in fifth?? & that B was the correct answer? pls let me know ! Thanks!

[ohthatpatrick]

Yes, it is totally wrong at the end! Wow, thanks for catching that. I'll go edit the original.