When the Idea of a challenge was first proposed by Icewynd, the number of balls was 14. There was then some discussion about the proposal by people who intended to take part, and opinions differed on how many balls we were allowed to choose.
http://www.lottoforums.com/lottery/anything-goes/13079-announcing.html
There are advantages and disadvantages for each possible option of how many balls to choose. With a high number of balls picked the chances of getting correct selections are much higher, but the need to make the right choices in a wheel using those selections is also more important, as the cost of covering all the numbers in real play can be enormous.
In the end, Icewynd decided on 20 balls as the number we were allowed to choose. Even with 20 balls it is surprisingly difficult to consistently get more than three correct balls.
So thats why its 20 !
