All chariot racers are musicians. Some chariot racers are soldiers. Therefore, some musicians are soldiers. Valid or Invalid?

Valid. Your second premise tells you that some chariot racer is a soldier. Let's call him "Alfred". So Alfred is a chariot racer and Alfred is a soldier. So Alfred is a chariot racer. This last fact, combined with the first premise, tells us that Alfred is a musician. But Alfred is also a soldier. So Alfred is both a musician and a soldier. Hence, someone is both a musician and a soldier. Which is your conclusion.

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