Hi Rich,

The answer is D ?

This is a strange question with no correct answer, and a little Googling turned up what seems to be its source. (DON'T pay attention to the explanation there, however, as it's incorrect.)

As Rich notes, the contrapositive is an important concept on the LSAT but a minor (perhaps irrelevant) one on the GMAT, which is much more about common sense arguments than about logical deductions. But if we're going to use the contrapositive, we ought to use it correctly, and the OA (which is B) is WRONG.

Here's the gist. The statement "If a, then b" is the SAME as the statement "If not b, then not a". To see why, consider the first statement: if a happens, then b MUST happen. So if b didn't happen, it's impossible for a to have happened: if a had happened, then b would've happened. (For instance, consider the statement "if I win the Nobel Prize, then I'll be famous". I'm not famous, so I must not have won the Nobel Prize.)

Now let's return to this odd argument. If Farmer Gil "correctly" observed that

"If something is a border collie, then that thing must be black and white"

then the obvious contrapositive of this statement is "If something is NOT black and white, then that thing is NOT a border collie". Since we're told Farmer Gil is correct, Farmer Geva has made an astute inference from a correct statement, and is ALSO correct. Nothing is wrong with his argument!

Now what I assume that the author of the question MEANT to have Farmer Geva say was "If something is black and white, then that thing is a border collie". That would be an example of mixing up necessary and sufficient conditions and would be an improper deduction from Farmer Gil's statement ... but if my aunt had a mustache, she'd be my uncle.

Matt said:

(For instance, consider the statement "if I win the Nobel Prize, then I'll be famous". I'm not famous, so I must not have won the Nobel Prize.)

The fact is Matt, that you are famous! You are Matt from G-Matt Mondays! Therefore your argument is false and since you are famous maybe you have won the Nobel Prize as well???

Seriously, though this is a strange question. Best to take Matt's advice and ignore this one.