It has the charm of old scale problems: few movements, very expensive information and a solution that must be clean from the beginning. It does not ask for brute force, but for a good distribution of uncertainty.
The wise men and the pearls (ancient Persia)
Riddle statement
A sultan has 9 apparently identical pearls, but one weighs a little more than the others.
He has a two-pan scale and wants to identify the heaviest pearl using the smallest possible number of weighings.
What is the optimal strategy?