There is an island with 12 islanders. All of the islanders individually weigh exactly the same amount, except for one (either weigh more, or less than the other 11). How can you find which islander is the one that weighs more/less than the others? You must use a see-saw to figure out the weights, and you may only use the see-saw 3 times max
Put 5 on each side, if the scale doesn't move, then it is 1 of the 2 you DIDN'T put on the scale. If it tips down, then take those 5 and split them between the scale of 2 and 2, and leave one off. If the scale doesn't tip then got it is the one you left off. If the scale tips down, take those 2 and put one on either side.