|Posted: October 8, 2010, 5:10 pm - IP Logged|
They divide the total amount of tickets by winners. For eaxmple: If there were 500,000 top prizes in 2,000,000 tickets, the odds would be 1:4.
With scratchers however, there is a catch. At the start, the odds of winning a top prize were 240,000, but when one(or two or three) of them is claimed the odds change. As prizes are won the the original odds(1:240,000 in your case) are no longer true.
Edit: I said "total amount of tickets by winners", but since we're talking about just top prize odds I may be wrong. I think top prize odds are calculated by dividing the total amount of loosers by the amount of top prizes. Either way if one top prize has been claimed those odds are no longer true.