Someone writes a bunch of random numbers down on paper and hands you three of them face down. You flip them over one at a time and have to stop when you think you have identified the largest of the three.
Move down for correct answer.
Flip over the first two.
If the second one is larger, stop.
If the second number is smaller, flip over the third one.
Performing this way gives you a .66 chance of winning.
Martingale? And when you have more than 3 cards? Or the number of cards is unknown? The trading looks like the situation when the number of cards is unknown.