Oleg is a math major or Oleg is an economics major. If Oleg is a math major, he is required to take Math 362. Therefore, Oleg is an economics major or is not required to take math 362.
I have to prove the validity/invalidty of the above argument, so I represented it with logical symbols as follows:
$$p \lor q ,\\ p \to r ;\\ \therefore \quad q \lor ~r$$
I built some cases from truth table: When p, q and r are true, p->r is also true and the conclusion is true. But when p and r are true and q is false, p V q is true, p -> r is true but q v ~r is false. This proves the invalidity of the argument? If not, what is wrong?
It doesn't mention whether or not Oleg is required to take Math 362. Not knowing that, we can't determine whether or not he is a math major. Plus, or is inclusive by default (the first option, or the second option, or both), so he could be both a math major AND and an economics major. Basically, not enough possibilities are considered to draw a definite conclusion so this is invalid.