Ok, this puzzle was recently posed by someone famous so don't search for it on the internet but give it your best shot - definitely trading related: You own a small casino in Las Vegas. It has 50 standard slot machines. Identical in appearance, they're identical in the function. They have exactly the same payout ratios. The things that cause the payouts are exactly the same. They occur in the same percentages. But there's one machine in this group of slot machines that, no matter where you put it among the 50, in fairly short order, when you go to the machines at the end of the day, there will be 25% more winnings from this one machine than from any other machine. What is different about that heavy-winning machine? Full disclosure: I had no clue before reading the solution.