Posts: 10 I am a woodworker, and am designing a two part magnetic/spring lock for my blanket chest. The first part has 3 master buttons (primary buttons A, B, C), and the second part has 11 secondary buttons (1, 2, 3, ....11). What you do first is choose 1 of the 3 master buttons that opens the first part of the lock. Then out of the secondary buttons, you have to choose button(s), but the user does NOT know how many buttons need to be pressed to open the rest of the lock. The user also doesn't know if the buttons have to be pressed in a certain order OR if they can be pressed again. So, not only do you have to choose the correct master button, but the secondary buttons as well. The master control that you choose stays depressed because of a lever, but each secondary button is spring-loaded so it pushes back out when you release it. The interior of the lock (the guts) is made up of springs, neodymium magnets, steel rods, and blocks of wood (Which really should not matter because it has nothing to do with the math problem). To sum up: You are choosing A, B, or C, and then some unknown amount of buttons #1-11. How many combination possibilities are there? Can this problem even be calculated?