We are given X->Y and asked what must be assumed to properly infer not Y->Z
Contrapositive: not Y->not X
If we have not X->Z we can properly infer the conclusion using not Y->not X-> Z
Contrapositive of not X-> Z is
Not Z-> X
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@julesc no! The contrapositive is identical in meaning so either would be the correct answer.
Notice that both options are not present because then you would have two right answers.
Hope that helps! Please let us know if you have any other questions.
P.S. You can see the explanation when reviewing these drills. Just tap "Daily Drills" from the left menu and then "review" on the set you want to review.
