Most people think mathematics is boring. I don't, but neither do I recall ever being as fascinated by mathematics as I was this morning, listening to a Melvyn Bragg discussion on probability as I drove home from Cardiff. One bit of the discussion I remember was to do with how many people need to be in a room for it to be probable that two will share the same birthday. Answer is 23.
It is mathematically provable that there is a probability that two of the participants on the field of play in a football match will share a birthday (that's if the ref is included). Or an international rugby team with its 7 replacements (and the ref again). It seems that 23 is the number of people needed, on average, to pass the 50% probability level. This is a much lower figure than I'd have expected.
But to reach a 50% probability that another person will share the birthday of a specific person in a room, it needs over 250 people. This is rather higher than I would have expected. So there is 'probably' no-one in the entire Gordon Brown fan club who share's the Prime Minister's birthday. Completely useless bit of information I know - but it interested me.