#7 - Global, Could Be True, List

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?f=160&p=87962#p87962)

The correct answer choice is (A)

The best strategy on List questions is to use the individual rules of the game to eliminate incorrect answer choices.

Answer choice (B) can be eliminated because from the third rule G and J cannot move the same piece of furniture.

Answer choice (C) can be eliminated because according to the second rule when J moves the table then M must move the recliner.

Answer choice (D) can be eliminated because from the first rule when H moves the recliner then G must move the sofa.

Answer choice (E) can be eliminated because from the first rule when G moves the sofa then H must move the recliner.

Answer choice (A) is thus proven correct by process of elimination.

[Tami Taylor]

Hello! I want to confirm why (A) is the correct answer choice for #7.

I read the post about the phrase "if but only if" in the "Setup and Rule Diagrams" topic. When I originally attempted this game, I didn't realize the phrase yields a specific conditional relationship (double arrow or bi-conditional relationship) between the two variables (Grace and Heather, in this case). Therefore, I couldn't eliminate AC (D), but now I think I understand why (D) is incorrect.

Is (D) incorrect because H is moving the recliner, but G isn't moving the sofa? Given the bi-conditional relationship, G should be moving the sofa whenever H moves the recliner. Is this correct?

Also, what is the contrapositive term for a double arrow statement?

Thank you!

[Dave Killoran]

Hi Tami,

Thanks for the message! Your reasoning here is exactly correct, well done!

The contrapositive of a double-arrow is the same double arrow but with both terms negated. So, it works like this:

• Statement: C D (C and D must occur together)
  
  Contrapositive: C D (or both C and D don't occur)
  
  This reflects the fact that double arrows allow for only two outcomes: both events happen or both don't happen.

Thanks!

[Tami Taylor]

Awesome! Thank you, Dave!

[Adam Tyson]

Hello!

I am frustrated with the first question, number 7. It seems like it should be so easy, but I have done this game a couple times and I always pick D. Can someone explain why D is wrong/A is right? I saw the "if and only if" and knew to diagram the rules with double arrows. However, I think I am getting stuck because I do not understand the contrapositive with a double arrow. A and D appear to me to be the same. Thank you in advance!

Ari

As with most "list" questions, Ari, you should attack it with the "rule by rule" approach. That is, look at each rule in turn and go through all the answer choices, eliminating from consideration any answers that violate that rule. Keep whittling down the options until only one is left, and then select it.

The first rule here is the biconditional between G moving the sofa and H moving the recliner. Either both of these things happen, or else neither of them does. Answer D violates this rule because it has H moving the recliner but does not have G moving the sofa. That's the first answer to be eliminated.

Answer E violates the same rule but for the opposite reason - it has G moving the sofa, but H is not moving the recliner. One rule down, two answers gone.

The second rule is a simple conditional. Look for a case where J moves the table but M does not move the recliner. Answer C is knocked out because that is exactly what happens there. Now we are down to just A and B.

G and J can never work together, but B has them both moving the table, so B is out and A, by default, is the correct answer.

The tricky part about answers D and E is that the first rule is a biconditional. Again, either both of those things occur, or else neither one of them does. Once you get that, eliminating that pesky answer D should be much easier!