Q16

[jamiejames]

Hi, I'm having a hard time on this question. I can see why E is right, but I can't see why B is wrong.

If U is first, that does this

U_ _ _ | _

And if U is in, that means that R cannot be 2nd, and if R can't be 2nd, and S can't be 1st (U is there,) 2nd (rule two), 3rd (if it goes 3rd, there's no place for the QT block) 4th (rule 2), then S does not run in the track meet.

Can someone explain which B is wrong?

[rshapiro14]

Because there are two frames for this question, if U is first

If U is in you know that R can't be 2nd, neither can S because of the second rule, and neither can U because it's already placed. So only T and Q can be 2nd. If you make two frames for this you get:

U T _ _ | _
U Q _ _ | _

In the first frame if T is second you know Q has to be out because if it was in it would have to be QT. From this you know that S and R have to be in because only one can be out. But S can't be fourth so it has to be third, and that leaves R for fourth.

U T S R | Q

In the second frame you know that T has to come after Q, and since S can't be fourth, there is no place for S to be so it's out. R is the only one left, he's fourth.

U Q T R | S

In both frames you can only have R fourth.

Since it's a must be true question make sure you're looking for something that HAS to be true and not something that could be true. Also since there are so few variables in this game once I figured out that two people couldn't run second I immediately made too quick frames with the two variables that could go second, T and Q

[monicaiannacone]

I got this question wrong- I chose B but now I understand why E is correct. However, this question took me several minutes- about 3 minutes to go through A, B, C, D, then E and do trial and error to find which 4 CBF and which 1 MBT. In this case, since the answer was E, this was a very time consuming question for me.

Is there a faster, less time consuming way to solve this question? (Aside from drawing all the frames to start- which I also tried when I solved the game another time. However, I found this MORE time consuming overall and almost a waste of time because of all of the potential options!)

In this case, would it be better to skip this question (since it took 3 minutes!) and use that time for the next game?

I had a similar problem with #15 since its a MBF question. But for #15, it was easier and less time consuming since the answer was A. Overall- is there a faster way to solve these MBT or MBF questions?

Thanks!

[timmydoeslsat]

While it may be inappropriate to frame an entire game, you should always be on the look out for framing opportunities within a question.

We are dealing with a must be true question stem, a local question telling us that U is first.



The first thing the local rule tells us is that we can trigger our biconditional of ~U<--->R2. We now know that R cannot be 2nd.

What we can see is that the placement of S is very limited. Before we entered the questions, we knew that S could only go 1 or 3 if it is to be in the race.

Now it is down to just 3 if it is to be in the race.

So I would frame this by showing what happens when S is 3 and what happens when S is out.



*I often, out to the left side, denote the variables that have not been placed left so as to keep track of my list.*

It is now time to consider the first frame. We know we cannot have a QT block. This means we cannot have Q. We now know that Q must be out. We now know that T and R must be in. We know the R cannot be 2, so that means that R must be fourth and T must be second.

As for the second frame, I know that with S being out, Q, T, and R must be in. Since we have a QT block and R cannot be 2, we know that the QT block will occupy slots 2 and 3, which will force R at 4.



This is what must be true in both scenarios, R being 4th.