If any of the organisms responds to two of the antibiotics, then which one of the following is true about such an org...

Emil-Kunkin on January 27, 2022

Hi Abigail,

This question is asking us about a scenario in which one of the organisms reacts to two antibiotics. We know from the final rule that Y responds to F, so we know that Y responds to both F and G. This is because (as you correctly noted) of our "if F then G" rule.

Since we know that it is possible (and not just possible, but mandatory) that we have an organism that responds to both F and G, we can begin to eliminate some answer choices. We know C is not correct since we have an example in which H is not one of the two to which our organism responds. We also know that E and D are incorrect since we can show a valid counterexample of F and G together. This leaves us with A and B- as you noted.

Since there are only three antibiotics, there are only three combinations that we could have in which one organism reacts to two. These are G and F, G and H, and F and H.

We already know that G and F is allowed, and we can thren test out F and H and F and G.

There don't appear to be any rules that would eliminate the possibility of G and H, but there looks to be a problem with F and H. If we have F, then we must have G. So if we have F and H, we must also have G making it FGH. We are told, however, that no organism can react to all three antibiotics, so FGH is impossible, therefore FH is not allowed.

We only have two valid combinations of two: FG and GH. Since both of these combinations have G, we know that if an organism reacts to two antibiotics, then one of them must be G.