I got this problem from Card Review section...
P1: A==>B
P2: ?
C: not B==>C
Ok, I see that after I wrote out the question I have "not B" from conclusion in common the "not B" contrapositive of P1.
I wrote it out like this: not B==>not A==>C then I wrote it in what I believe to be the contrapositive: not C==>A==>B
I made the assumption that the answer was "not C==>A based upon the previous question which was the same thing (see below)
P1: X==>A
P2: ?
C: not A==>B
again you have in common the "not A" from conclusion with the contrapositive of P1. I wrote out as such: not A==>not X==>B then I assumed the correct procedure was to rewrite it in reverse as such:
not B==>X==>A
The correct answer with the problem was "not B==>X"
The correct answer in the first question is "not A==>C, I assumed incorrectly. What am I doing wrong?
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You haven't done anything wrong! Remember that a contrapositive carries the exact same logic as its counterpart. They are interchangeable. So, when the correct answer to your first problem is listed as (not A - -> C), (not C - -> A) is also an acceptable answer. Usually, the flashcards will list both versions of the correct answer.
I wrote the same answer that you did for your second question: (not X - -> B). When I see that the listed answer is the contrapositive of my answer (not B - -> X), I know that I have answered the question correctly.
