p. 7-39, #5

[TargTru99^]

Greetings,

I put B notA for the answer to this question, but the answer key says that it is notA B instead. Would my answer work just as good? If not, what is the problem with it? Please let me know ASAP. Thanks!

[Robert Carroll]

Targ,

Your answer is a Mistaken Reversal of what's required. The answer key is correct. "B A" is also an acceptable answer, as it is the contrapositive of the answer key's conditional. The resulting chain is:

A B C

Which of course proves A C.

Robert Carroll