偶然

What are the chances of me bumping into my sister in law in a train in Tokyo.

Calculate:

1. Possibility of me having a meeting around Roppongi-1-Chome
2. Having a few drinks with our partner
3. Chatting with my work colleague before departing
4. Deciding to walk to Ginza line
5. Boarding a very busy train
6. Turn around and see my sister in law

Amazing!