The 12 balls puzzle, also known as the twelve balls problem or weighing puzzle, is a classic logic puzzle where you must identify one odd ball among twelve using a balance scale in only three weighings.
Here is a classic brain-teaser puzzle from 1945: You are given twelve identical-looking balls and a two-sided balance scale. One of the balls is of a different weight, although you don't know whether it is lighter or heavier. How can you use just three weighings of the scale to determine not only what the different ball is, but also whether it is lighter or heavier?