I'm a salesman and I have a list of 100 addresses all equidistant from each other and from where I'm standing right now. (I know this is impossible in 3D space but just let's assume it is to make travel times equal). I only have time to call to 10 houses so I want to maximise the chances that I'll call to houses where someone is home. For each address I know: 1. The time when someone was last known to be home (not necessarily the last time they were actually home) 2. The last time a call was made How do I choose the 10 houses?