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So it looks like in 1967 the dimes and quarters were either 80% silver or 50% silver and then in 1968 the dimes and quarters were 50% silver or 99% nickel. How do you figure out the 1967's? I think I can use a magnet on the 1968's to remove the nickel ones.

The 67's you can't tell the difference without melting them. They are actively traded as 65%.

What he said. Also, yes get your magnet out to remove the nickel coins. nearly every one you find from 1968 will be nickel but I've found a little silver before.

The magnet is tireless and never lies about the metallic content of the 1967-68 dimes and quarters. I thrive on finding even the 50% silver coins in a stack of tired-looking accumulation or bag of Canadian dimes or quarters. These are an often-ignored segment of the available silver-in-the-wild. Most people don't even know what to charge for this. Even a low-ball offer sounds good to the source.