You may not have noticed but the Sainsburys Active Kids vouchers have a 15 digit code printed on the bottom of the front face that you can enter in to a draw on their website.
Every five minutes between 8am - 10pm until 3 June 2009 they are giving away £50 of vouchers to someone who entered a code in that time window.
And the other night I won! Sweet!
So how lucky was I? According to Wikipedia their annual revenue is around £20 billion.
Daily that's around 20 billion/363 = 55 million. Vouchers are given out for every £10 spend. Assume half of the revenue results in a voucher being given out so the number of vouchers issued per day is around 2.75 million.
I've no data on which to base the fraction of vouchers that get entered in their Draw. Assume only 1 in 10 as most people I've spoken to hadn't noticed this feature and lots of people won't be bothered.
If the codes are entered evenly over the period, which I'm treating as being the same thing as saying that those issued on a day will be entered on a day, then the number entered every 5 mins is 2.75 million / 10 / (14*60/5) = 1640.
So my odds of winning a draw were approximately 10/1640 = 1 in 164. Lucky me.