Which one of the following could be true?

zia305 on July 15, 2020

Explanation

Can someone please explain this answer?

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shunhe on July 15, 2020

Hi @zia305,

Thanks for the question! So we’re asked here which one of the following answer choices could be true, and we’re not given any other information. So we have to be able to figure this one out from the diagram. First, we should look for answer choices that are easier to eliminate/involve variables that are more restricted.

When setting this game up, we should’ve noticed that there’s only 3 slots T can go in. Chapters 2, 3, and 4. Rule 1 tells us T can’t be in chapter 1, and rule 2 tells us that T has to be before W by at least two chapters, so T can’t be in the last three chapters (since there wouldn’t be room for W). That means T can’t be chapter 5, so we can get rid of (B) pretty quickly. Also related to the second rule, W can’t go before chapter 4, again because T has to precede it by at least two chapters, so (D) is also easily eliminated.

Now we’re left with rules (A), (C), and (E). And notice that there are no rules relating to rule R, which means that relatively speaking, rule R is pretty free. So we can try out (A) first and see if we can come up with a scenario that works. And we can, actually. Consider the following:

ZTXUWSR

This doesn’t violate any of the rules, and places R in 7th, so (A) is the correct answer choice here.

As for why (C) and (E) are wrong: let’s say we put U in 7. Then we have to put X in 6 based on the last rule. And now W can’t be in five because of the second-to-last rule, so W has to be in four. But that forces T in 1, which can’t happen based on rule 1. So (C)’s impossible.

Now let’s say we put X in 6th. Again, that means W can’t be in 5th or 7th. Which means W can be at latest 4th. But again, that would force T in 1, which can’t happen.

Hope this helps! Feel free to ask any other questions that you might have.

zia305 on July 18, 2020

Thanks for the help!

shunhe on July 20, 2020

Happy to help!