How small is this planet???

I lived in Perth, in Western Australia from 1971 to 1984. I completed high school and an undergraduate degree, got my first job, and in 1984 I moved to Canberra in the Australian Capital Territory. In 1985 I moved to Sydney, in New South Wales. I've been back to Perth a few time, usually for work, but I have made no attempt to stay in touch with the people I went to school with.

There are currently around 20 million people living in Australia.

So I'm in Western Australia, for an all too brief holiday, and we've detoured to the Capel Vale Winery, to taste and buy wine, and to get lunch in their (excellent) restaurant. It's a lovely place, you can see part of it on the right of this picture - the restaurant overlooks part of the vineyard:


When we've finished eating, someone at another table calls out to me. It's Gillian Mills - we went to high school together. I wouldn't have recognized her, though she says I haven't changed a bit (in 31 years? Hmm.....). She's in Capel Vale as part of a book club event, she doesn't live locally - we're 3 or 4 hours drive south of Perth.

Anyone care to calculate the odds on meeting up like that?