Why is the pictured argument valid?
Velleman in this chapter section says that an argument is valid only if the conclusion has the option of not being true if all the premises are true.
But row 7 is the only row where all three premises (Premise 1 - "P1", Premise 2 - "P2" and Premise 3 - "P3") are true yet the conclusion (last column "C" or "P") is false.
This shows the argument is invalid. I'm not sure why Velleman has this as valid?
The argument is valid, no matter how you look at it.
The mistake is where it writes "Pete win Chemstry price is represented by P".
Actually, you will see it is represented by C before, and if you copy the colunm C, nothing weird happens.