Strong Vs Valid Arguments

So for a strong argument I am using an example from my dad. Ever since he moved into a new condo he has gotten a bad rash. Other than this new condo, every place he has ever lived at he has not gotten a rash. Therefore he believes that some chemical or fibers in the condo are making him break out in a rash. Now I believe this is a strong argument because the premise is very true because ever since he moved into the condo he has gotten a red rash all over his body, something that he has never gotten before. However the conclusion may be false. There are many possibilities why he has gotten a rash living at this specific area. He may be alergic to the large tree's pollen that is outside of his window that is open all the time. There could be a fungus left over from the previous tenants that he was exposed to. So there are many possibilities why this conclusion may be false, therefore making it an invalid argument.

For a valid argument I am going to use an example from my life. The law school I want to apply to requires one to take the LSAT exam. Every student at this law school has taken the LSAT. Therefore I have to take the LSAT to get into this law school. This is a valid argument because the premise is true and the conclusion is true at the same time. An invalid argument would have a true premise but a false conclusion.

So we see that the main difference between the two is the conclusion. The premise must be true and so does the conclusion in order for it to be a valid argument. On the other hand the premise is true for a strong argument but its conclusion may be false. Also you can reword the same argument to make it either valid or strong.