Mark,

I almost understood the lottery situation :).
Now consider this situation:
The total number is 200
You should select 2
The time period is 20 days

The probability for each day is ??????
2/200 *1/199 - according your formula
1/200+1/199 - according mine (now I seriously doubt in this formula)

Now, for the whole time period probability is ?????
?
?



>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