Logical reasoning PrepTest 111 · Section 1 · Question 22

Incorrect. Hominidae → Tracheophytes. To get this to line up with the conclusion, we can take the contrapositive—not Tracheophyte → not Hominidae. And, from there, we can see that it negates the sufficient condition that would work as a sufficient assumption.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
Chordate → not Tracheophyte
Pteropsida → Tracheophyte
Therefore — Pteropsida → not Hominidae

Answer Anticipation:
This Strengthen with Sufficient Premise question is all about the conditional logic.

First, let's talk about our diagram. The second premise is relatively straightforward (with "all" being the same as "if") but the first and last can be tricky. A statement saying No As are B can be diagrammed as "If you're A then you're not B" or "A → not B" as we did.

With that established let's work through the logic. We can see that the sufficient condition of the conclusion is featured in the premises but the necessary condition isn't so we'll need to connect a premise term to not Hominidae. Building from Pteropsida and taking the contrapositive of the first conditional (instead of the second since the second lines up with the conclusion) we get:
Pteropsida → Tracheophyte → not Chordate

Now we just need to connect the end of the chain to the necessary condition of the conclusion:
Pteropsida → Tracheophyte → not Chordate → not Hominidae

So our answer will be that last link or its contrapositive:
not Chordate → not Hominidae
Hominidae → Chordate

Answer Explanation:
Hominidae → Chordate. This answer matches the contrapositive in our anticipation so it's the correct answer. If all P are T and all T are not C and all not C are not H (the contrapositive here) then all P are not H as the conclusion states.

Key Takeaway:
Being solid on conditional logic can make a question like this take relatively little time so be sure to practice it!

Also No As are B translates to A → not B.

Incorrect. Tracheophyte → Pteropsida. This answer reverses the second conditional premise.

Incorrect. Hominidae → not Chordate. Close! But it negates Chordate, whereas the argument assumes that all H are C.

Incorrect. Chordate → not Pteropsida. This answer is already established as true through chaining the two conditionals together.