One marble is different in weight (lighter or heavier).
How do you find which one?
(more clues to answer below)
3 places to put the marbles,
Balance Scale [left side, right side] , and on the table.
3 states for the balance Scale: left side goes up, left side goes down, no movement.
The full answer is very elegant.
Very fun to write down.
Then more questions come up, like: how many trials are necessary for 13 balls? 16? 30? any random number?