9 LEE wrote:
120 individual prizes for 550 members. If we had a one Prize Draw with 120 prizes up for grabs, and 550 'entrants' - what would the odds be? That's the same odds but spread over a year, surely?
Yes, but it just makes it harder to count - keep it as 120 draws with one prize each, please 🙂
The way I see it is, since the draws are completely independent random events,
- the probability to win a prize in a single draw (of which we have 10 each month) P1 = 1 / 550
- the probability to not win a prize in a single draw (ditto) P2 = 1 - (1 / 550)
so the probability to win one and just one prize in 120 draws is then
P = (P1 * P2^119) * 120 (because we need one win and 119 non-wins, and the win can be any of the 120)
~= 17.57%
Of course, the real probability for winning at least one prize is larger, because you are not excluded once you have already won. Unless we want to get into binomials, it's easiest to calculate the probability of not winning even once and complement that, so the answer to the original question is
P = 1 - (P2 ^ (12*10)) ~= 0.196 = 19.6%
Likewise, the chance of me not winning a single prize in all my past 17 draws is then P2^(17*10) ~= 73%, which probably explains it all 😎