Thanks very much to both of you. I've implemented both methods and they both work nicely.

Just for your own amusement, the reason I'm doing this is because I have a few friends who like a bet on the horses, and every now and then convince themselves they've found a tipster who is the messiah. Knows what others don't, can tell the future etc etc!

I know that if there was any such person, who could consistently predict winners in any form of sport (especially horse racing), they would either keep very quiet about it and retire to the Bahamas before too long, or they would want a fortune for their services. They probably wouldn't be involved in excessive and highly suspicious forms of self promotion on Facebook, claiming they win thousands every day with "evidence" that a 5 year old with photoshop could fabricate in order to receive $10/month from punters for their knowledge. But when I point this out I am called cynical.

So I thought one way to debunk (or maybe prove!) the myth than by pitting the self proclaimed knowledge of this particular tipster with hundreds of thousands in claimed winnings, and years of experience, against a humble excel formula based on nothing more complicated than the book makers odds, and random chance.

I'd be happy to share the results with anyone who is interested!