As it is presented in the passage, the approach to history taken by mainstream U.S. historians of the late nineteenth...

Molly on October 11, 2019

Game 4, Q 15

Hello, on question 15 (the trains) I am not sure why E is the answer. It looks like no answer "must be true".... If the rules state that either Y OR W could be 4th, then it could be true that W is before Y, but I don't understand why it must be true. I understand that based off the hypothetical in 14 it makes sense, but it doesn't make sense to me given the set of rules. Can you explain that? Why would the rule be that W or Y could be in 4, if it must be true that W comes before Y?

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Irina on October 11, 2019


The game requires us to determine the order of seven trains - Q R S T V W Y.

___ ___ ___ W/Y ___ ___ ___
1 2 3 4 5 6 7

The rule that tells us that W must arrive before Y is rule (2):
S arrives at some time after W and before Y. The only way S could arrive after W and before Y is if W arrives before Y - W S Y -, hence we can conclude that it must be true.

Let me know if you have any further questions.

Molly on October 12, 2019

Wow I totally didn't even see rule 2 there.... that's how I know it is time to take a study break haha.
Thank you for explaining!