While wailing away the hours I've put my mind to a problem posed by newly minted Mauritian FM Roy Phillips (7/10 at the Olympiad!): Out of 12 balls, identical in appearance, one is of a slightly different weight to others. You have a set of balancing scales. How do you find the (a) odd ball out and (b) determine it is either heavier or lighter than the others, using the scales only 3 time?
He says he eventually solved it but for now I don't have an answer.