Nope. You have 2 chances that the selected "ball" is your "number." To get it, look at the lottery analogy. I have picked 6 numbers. I have 6 chances that the first ball drawn, out of a 50 possible balls, will match 1 of my 6 numbers. I now have a match on the first draw. That was 6 out of 50. Now 49 balls and 5 numbers remain. I next have 5 chances that the next ball will match one of my 5 remaining numbers or 5 out of 49. So the progression I gave you is correct for the lottery. Transferring that logic to the beauty contest is valid.

>Mark,
>
>>If 2 are selected then the probability is:
>>
>>2/n * 1/[n-1]
>
>This is obviously not right. If the possibility of one to be selected of n is
>1/n (obvious), then the possibility to be one of 2, who selected, should increase (not decrease, as in your formula).
>so, it should be 1/n + 1/[n-1], as I understand.
>
>
>
>>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.
>
>Ok, it's probably right.
>
>What about other kind of lottery, there each number could be from 0 to 9,
>say 000000
> 999999
>any number between them.
>The probability is 10 in -6, as I understand, so greater, than in State Lottery, which also seems to be non-obvious. Or am I wrong?
>
>>
>>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