[mgillett]

One that I heard last week: There is an 8x8 checkerboard in a room with a coin placed on each square. Each coin is either facing heads or tails up, and the face is determined randomly. Before you can inspect the board, a "master" comes in, picks a square of interest, and must make a manipulation to the board by flipping one of the 64 coins. He then exits the room. You are now allowed to enter, and must read out which square of interest the master chose by inspecting the state of the board. There is a strategy that is guaranteed to work for all possible configurations of the board.

[agf]

I think you're referring to this puzzle: http://datagenetics.com/blog/december12014/index.html

The version you gave is missing information and so can't be solved as stated.

[kristjansson]

Thank you for posting this. I read the parent several times trying to figure out if they were mistaken or I was dense.

[CPLX]

I had to read that like 11 times before I started to get the underlying principle. That's amazing.

[hexane360]

In a very similar vein, try this one: https://youtu.be/N5vJSNXPEwA

[dpark]

Either I'm somehow missing some critical piece of this puzzle or your description is. The master could pick a square at random, leaving you with a board (and likelihood of success) that is still completely random.

Are you supposed to be collaborating with the "master"?