Nigel Parsons solution only works if each monk is (a) as clever and logical as Nigel Parsons and (b) is prepared to assume that all the other monks are as clever and logical as Nigel Parsons. There is nothing in the wording of the question to suggest this is the case. Many of the monks may be as thick as two short planks, and many of the other monks will know this as they all live together. In which case, Nigel's solution falls down. Orry, but that's logical.