Therefore, the maximum number of wins expected for 1000 people with odds of 1 to 20 is 50. So, first of all, 1 to 20  odds is actually equivalent to 1 in 21 people winning, not 1 in 20 people winning.

When you see the odds presented as 30:1 or 3:1 that's actually just showing the payout for a winning bet, not the likelihood of that team winning. 30:1 doesn't mean that the team is 30x more likely to win, it means that if you bet on that team and they win you will receive $30 for every dollar you bet.