Answer: (1) Some teachers are not Mathematicians — NOT valid.

Easy check:

• Teacher ⇒ College Graduate, and no graduate is poor ⇒ Teachers are not poor → (4) valid.

• All Poets are poor; graduates aren’t poor ⇒ Poets aren’t teachers → (3) valid.

• Some Mathematicians are Poets ⇒ they’re poor ⇒ not graduates ⇒ not teachers → (2) valid.

• (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.