The correct answer is the Lamisil. Approximately 7 days, and it's gone.
What I do? Lamisil through out the day, then soak a cotton ball in Apple Cider Vinegar at night and tape it over the ring worm with medical tape. If it's working your will get a stinging sensation on the ring (if it becomes a burning sensation in the general area, then congratulations you've left it on too long and now have a nice little chemical burn). You should soak the ringworm in ACV until the ring area whitens, then remove the cotton ball, and allow it to dry.
Next day apply Lamisil again (chances are the ring may already be scabbing up a little, but you really should do two days), then when you get home at night, same treatment with the ACV (until the ring whitens, you'll probably find it does so faster, and more of it will whiten the second day). Allow to dry again, and congratulations the RW is dead.
If ACV is applied in the right amount for a long enough time it will dry out, the ring will become like a thin scab, and a couple days after the treatment it will flake completely away. To be on the safe side you may want to apply the lamisil for a week after treatment.
Also, don't forget to wash everything after every use when you have RW! Towels, sheets, pillow cases, all clothing, etc. It is common to reinfect yourself during treatment.