Question 15
(MEX 2) Determine for which positive integers $k$ the set
$$X=\{1990,1990+1,1990+2,\ldots,1990+k\}$$
can be partitioned into two disjoint subsets $A$ and $B$ such that the sum of the elements of $A$ is equal to the sum of the elements of $B$.
$$X=\{1990,1990+1,1990+2,\ldots,1990+k\}$$
can be partitioned into two disjoint subsets $A$ and $B$ such that the sum of the elements of $A$ is equal to the sum of the elements of $B$.