Q5

[Aliyachisti9]

Could someone explain how E is correct? I know that N, K, P, G all can go first, but I guess I am a little confused with the wording for answer E since it is a MUST BE TRUE question.

[timmydoeslsat]

This is a global question asking what must be tree of our tree diagram.

You are correct that KPNG can all go first. However, it must be true that no more than four can go prior to N.

Think about which variables it could be that could go prior to N. It could not be H, O, or L. That leaves G, P, K, and I. So that is exactly four variables that could go prior to N. This means that it is impossible for more than four variables to precede N.

[ohthatpatrick]

Great response.

The flipside of how you can see (E) must be true is to think about what MUST come after N.

Hopefully as you chained together the ordering rules, you ended up with
N - H - O - L
somewhere in your chain of rules.

This means that the latest N can ever go is 5, because three things must still come after N.

When you're doing a must be true question, you can always evaluate the answer by asking yourself, "Can I avoid doing what this answer is saying?"

Since (E) says no more than 4 come before N, it's saying "spot 5 is N's latest possible spot". You could ask yourself, "could N go 6th?" Since N can't go 6th (as 3 things must come after it), you know that (E) must be true.

[hnadgauda]

I realized i had trouble on this question due to the wording of the answer choices. For Must be true questions, we can see if we can avoid doing the answer choice in order to eliminate it. So this means...

A: Can 0 valves go before P is opened? (Opposite of at least means going below the number).

B: Can 1 or 0 valves go before G is opened?

C: Can more than 2 valves open before O is opened? (Opposite of no more is more! )

D: Can more than 3 valves open before H is opened?

E: Can more than 4 valves open before N is opened?