If 2 are selected then the probability is:

2/n * 1/[n-1]

In our State Lottery, you have to pick 6 out of 6 numbers from a total of 50 numbers, that probability is:

6/50 * 5/49 *4/48 * 3/47 * 2/46 * 1/45 or about 16,000,000 to 1 for a payout of only $4,000,000 or less.

I am sure someone can provide the simple formula, like x = n!/[[y-1]**[n-1]] -- which this example is not correct. It's been about 15 years since I had Differential Equations.

>So, I may hope? :) BTW, have you already been the Member of the day? I don't remember...
>
>So, the probability may be calcualted as: (right?) in each particular day for each such person:
>prob=1/337+1/336, if all these people had access in the last 20 days in each day.
>
>Let's count for simplicity 2/200 or 1/100.
>
>This feature started from Feb. 19th, say, 20 days.
>How will be prob calculated in this case? I never studied theory of probability seriously :(
>
>TIA