The numbers have been written on a board. Each time, one is allowed to erase two numbers, say, a and b, and replace them by the number . After 1999 such operations, one obtains exactly one number c on the board, than which of them is correct
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If we take a trivial case then it shows us the answer. If we think everyone comes and take the first pairs. I.e 1000&1001. Then second one takes 500&1001. And thus they continue. Then after 1999 operations the number left will be very less at about 0. Obviously less than 1.