Answer: (1) Some teachers are not Mathematicians — NOT valid.
Easy check:
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Teacher ⇒ College Graduate, and no graduate is poor ⇒ Teachers are not poor → (4) valid.
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All Poets are poor; graduates aren’t poor ⇒ Poets aren’t teachers → (3) valid.
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Some Mathematicians are Poets ⇒ they’re poor ⇒ not graduates ⇒ not teachers → (2) valid.
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(1) doesn’t follow: we’re told nothing about teachers vs mathematicians (and there might even be no teachers). Hence (1) is not a valid conclusion.
