It is hard to find a good puzzle nowadays, as even easy ones claim to be "impossible." However, this logic problem involving people trapped by a logician is going to require all of your brainpower. The situation is set up with 2 people trapped, where each can see a select number of trees. In order to escape imprisonment, each person has to say the total number of trees on prison grounds. It may sound simple now, but watch the video below to grasp the puzzle in its entirety.
The situation discourages guessing, so Alice and Bob have to use perfect reasoning to escape the puzzle. At first glance, the problem seems like there isn't enough information to possibly give a correct answer, but not so fast.
The key here is to figure out how to convey information to the other prisoner without expressively communicating. The only variable each prisoner has in their day is the act of the logician coming and asking them each a question. In doing so, each prisoner knows that on the previous day, the other did not guess or select the right answer. The act of Alice passing means that bob knows that she does not see more than 18 trees. This deduction from predicting how the other must think, is what will eventually set the prisoners free.
[Image Source: MindYourDecisions]
While solving the problem means that the prisoners need to go through 5 days of being asked the same question. Only then, is it possible to figure out how many trees there are in total on the prison grounds. Did you figure it out without having to be walked through?
Written by Trevor English