This puzzle was first published in 1889 by Joseph Bertrand in Calcul des Probabilites. And it's well worth another look.
Dressing it up slightly from its original, there are three chests of drawers each with two drawers. Each chest contains two pieces of gold, two pieces of lead, or a piece of gold and a piece of lead. And each piece of metal is in a separate drawer.
You are only allowed to open two drawers.
If you strike gold with your first choice, what is the probability that the other drawer in that chest of drawers also contains a piece of gold?
Answer at 9.00 on Monday