PT82.S2.G4 - A teacher will assign to each of three students

trotter.kyung

I just have a question about Rule 3 which is, M-->S Contra: /S-->/M. Doesn't this mean that M and S always go together? If so, then how can number 23 have S and J together without M?

Thanks

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ariincharge

I haven't seen the game and I will take a look shortly, but it sounds like this:

M --> S Contrapositive: /S --> /M means that if M then S but not the other way around. It sounds to me like number 23 has S and J as part of an answer choice which would be satisfying the necessary which does not trigger the rule AKA is irrelevant and M becomes a floater that could be in that AC or not in that AC. Hope this helps!

AudaciousRed

M->S. Okay... So.. if you don't have S, you can't have M. /S->/M Because you can't fail a necessary condition and the sufficient still stand alone.(Think of it like a truth table. You can never have all true premises, and a false conclusion. But can all your premises be false and a conclusion true? Sure. A true conclusion can stand on it's own)
However, Can you just have S? Sure. What happens if you just have an S? At no point does that rule say "If S, then M", right? If just says if there is NO S, then there is NO M. So, S could be on it's own without M, because the rule did not say that it couldn't. The only time they force each other to be with one another, both in and out, is S<->M. The same can be true of both letters being out. Can M be out and S be out? Sure. that could happen, because our rules don't forbid it.

When you chain your conditionals, if you have an element, it triggers all the elements forward of it.
A->B->C->D->X If you have A, it triggers down the line and gives you everything through X.

If you don't have an element, it nullifies everything directly BEHIND it.
A->B->C->D->X If there is no D, you cannot have C, B, or A. However, could you have X? Sure. That's possible. X could stand on it's own just fine. NOT having something only affects the letters BEHIND it in the chain, not after it. So, X is free to be or not be in this case, because /D doesn't impact anything in that direction.

I hope this made more sense This concept bites a lot of people in the butt, and LSAC counts on it throwing people for a loop.