Probability question

[Akverno]

Oh, what's the name of this if I remember right, conditional probability or some such nonsense. The classic stats example is you get to choose door number 1, door number 2, door number 3. Only one door has a prize. After you select 1 the host says let's look behind door number 2. Door number 2 doesn't show a prize. Then the host says would you like to change your choice, statistically you have a 16% better chance of getting the prize if you switch your pick to number 3. Damned statistics.