Option 1:
Use the last two digits of some commonly available public number that was, essentially, random or at least unpredictable and not controllable. A good example today would be the cents portion of the SP500 index.
Options 2:
Tally up which of the numbers had the least amount of money bet on it and then make that the number.
You can guess which of the two options the more nefarious organizations used.
Interesting related note: back in the first half of the 20th century, there used to be a game in the newspapers where you were presented with a grid of faces, each one being numbered. The goal was to pick the face that you though OTHER people would pick most often. In other words, if you picked the most popular face, you would win. This led to lots of "well which face do I think other people will think is most popular etc"
John Maynard Keynes used the game above as a proxy for the stock market with stocks being the faces e.g. you were trying to pick the stock you thought that everyone else would buy.