I have a rare coin that’s worth a bazillion dollars and I’ll give you and a buddy a chance to win it.
I’ll bring you (but not your buddy yet) into a room where I have a bunch of coins lined up in a row, probably randomly distributed between being heads up and tails up, and I’ll tell you which coin among those is the bazillion dollar coin. Then you’ll exit the room and your buddy will come in through another entrance (so you can’t communicate after I tell you which is the bazillion dollar coin) and tell me which coin to give to the two of you.
That wouldn't be a very fair game, so you can also tell me to flip whichever coins you want before you leave the room and your buddy comes in. (I’m flipping them myself to make sure you don’t send codes with subtle placement of the coins or such tomfoolery.) But you have to watch 10 minutes of Nyan Cat for every coin I flip so you want to minimize the number of flips lest you go insane. I’m not saying beforehand how many coins will be in the room, and you only get one minute to tell your buddy a strategy (just words that can be spoken in under a minute, no written cheat sheets) before it’s time to play the game.
Clock starts now.
(I would credit the source of where I heard the original form of this puzzle that I'm modifying, but I can't remember the source any more.)