Q22

[GeneW]

Why is A incorrect and B correct? In A, if an organism responds to F, then it must respond to G thus satisfy the condition of responding to two antibiotics.

For B, if an organism responds to G, it does not have to respond to F (or H). Is that right?

Any help would be appreciated. Thank you.

[christine.defenbaugh]

Great question GeneW!

I think what is confusing you about this question is in how you are relating the conditional to the answer choices. For conditional questions, you must take the conditional statement as absolutely already true, then determine what you know (and don't know) from that conditional.

It sounds like you are taking each answer choice, and checking to see whether it always satisfies the conditional. We want to take the conditional and see if it always requires the answer choice. See the difference?

In question, we're given the conditional "If any organism responds to 2 of the antibiotics", so let's start there and follow the inference chain before we deal with the answer choices. What are the possibilities for responding to 2 antibiotics?

options: fg, gh, or fh!

But wait - Rule 5 tells us that f will drag in g to the group. That means the 'fh' pair would become 'fgh', and that is not okay! (Breaks Rule 2, that no one can respond to all three antibiotics).

So that leaves us with only two options for 'responds to two antibiotics': either fg or gh.

The only thing that we know for sure must be true about an organism that responds to 2 antibiotics, is that it must respond to g, so (B) must be true. Antibiotic g is in both permissible options!

(A) The organism could respond to gh, so it doesn't have to respond to f.
(C) The organism could respond to fg, so it doesn't have to respond to h.
(D) It could respond to fg
(E) It could respond to fg or gh. It must respond to g.


Now, notice that what you said above is true - having g does not force an organism to respond to 2 antibiotics. But that's not what the question is asking. The question asks whether responding to 2 antibiotics forces the organism to respond to g. And it does!

It's critical to start from the conditional and see which answer choice must be true, rather than starting with the answer choices and seeing which one satisfies the conditional.

Please let me know if this completely answers your question!

[GeneW]

Thank you for the detailed explanation. It's very helpful. I see it now. Thank you. I greatly appreciate it.