I'm sure there have been instances where applicants with 1 interview have matched or more than 20 didn't match. But in general, how many interview invites should applicants strive to obtain.
Hard to say. Depends on how strong an applicant you are. I know a guy with 10 who didn't match. Couple people with less than 10 who did. I'd say midteens is pretty safe. If you are weak, the more the better.