MANY! Probably 15-20! Why should you apply to more than one school? Because it dramatically increases your chances of admittance!!!! Consider a situation where you have a 50% chance of admittance. Like winning a game based on a single coin flip, you have a one in two chance of ‘winning’ (getting into medical school) if you only apply to one school. But if winning the game requires that you only get a ‘head’ once, then flipping the coin multiple times is a great advantage; if you flip the coin twice, you have a three out of four chance of winning and if you flip the coin four times, then you only have a one in sixteen chance of not winning. Obviously, getting into medical school is not a mere matter of chance. However, some aspects of the process are.
In any group of applicants, there are a few applicants that would always get in anywhere they applied and a few more that would never get in anywhere they applied. But there is a substantial group in the middle that will get into some schools, but not all. Why? Not because the admittance committees flip coins, but because the schools and committees weight and evaluate pieces of an applicant’s record differently; even within schools, different committees will be different; even the same evaluator will rank students differently depending on ‘chance’ factors (how much sleep they got the previous night, what the previous application was like, etc.). Your best weapon to guard against the vagaries of the admittance process is to apply to multiple schools.