@RISHABHKASHYAP1 I was basing this on the "Let's Review" section at the end of the lesson. I assume that the contrast between those two is the takeaway since that's what they gave us.

Tricky one. I'll give putting this into words a shot.

A - NY Phil violinists

B - People who know how to play

C - People who are not exceptionally good

1.... (valid)

"A —m→ B → C yields valid conclusions via the chain.":

Premise 1 (A —m→ B) - Most violinists at the NY Phil (A) are people who know how to play the violin (B)

Premise (B→C) - All people who know how to play (B) are not exceptionally good (C)

Conclusion: Some (most) violinists at the NY Phil (A) are not exceptionally good at playing the violin (C)

2.... (invalid - this is originally given to us)

"A → B —m→ C yields no valid conclusions via the chain."

Premise 1 (A→B) - All violinists at the New York Philharmonic (A) know how to play the violin (B).

Premise 2 (B —m→ C) - Most people who know how to play the violin (B) are not exceptionally good at playing the violin (C)

Conclusion: Some violinists at the New York Philharmonic (A) are not exceptionally good at playing the violin (C).

(Incorrect because we don't know if the NY Philharmonic violinists are part of the "most people who know how to play violin" group.)