Let S be a subset of {1, 2, 3,............, 9}, such that the sums formed by adding each
unordered pair of distinct numbers from S are all different.
For example, the subset {1, 2, 3, 5} has this property,
but {1, 2, 3, 4, 5} does not, since the pairs {1, 4} and {2, 3} have the same sum, namely 5.
What is the maximum number of elements that S can contain?
unordered pair of distinct numbers from S are all different.
For example, the subset {1, 2, 3, 5} has this property,
but {1, 2, 3, 4, 5} does not, since the pairs {1, 4} and {2, 3} have the same sum, namely 5.
What is the maximum number of elements that S can contain?
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