The numbers are arranged as in some order.
Find the maximal possible value of
(Yahor Dubovik)
Solution
Note that the sum of all numbers is , so the required sum can be presented as the sum of the following two sums:
and
Let's bound each term of each sum separately. If are pairwise distinct elements of the sequence given in the problem statement, then
Moreover, this estimate is reached when or . Hence
So, the maximal possible value of the original sum is equal to
This sum is reachable if the numbers are arranged in ascending or descending order.
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