For the coin one, you have to separate them into groups of 500 piles, right? Hmm. Nevermind. I reread the riddle. Let's see... 980 O 20 X Required: 10X......10X and any number of O. One moment... "Count twenty coins into one pile, flipping each one over on the other side as you do so. That is your first group. The rest are the second group. No matter which coins you choose, the number of coins facing heads-up in both piles will be equal." Well damn, you're right. Next riddle.