Posted by **Lisa** on Tuesday, February 7, 2012 at 7:37pm.

Which argument is not valid?

1.) Given: a→b

a

Conclusion: b

2.) Given: a˅b

~b

Conclusion: ~a

3.) Given: a→b

~b

Conclusion: ~a

4.) Given: a→b

b→~c

Conclusion: a→~c

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