perplexus.info :: Numbers : Minimal cardinality

Minimal cardinality (Posted on 2016-03-16)

Let S be a set of n distinct real numbers.
Let A_S be the set of numbers that occur as averages
of two distinct elements of S.

For a given n >= 2, what is the smallest possible number
of distinct elements in A_s?

Submitted by Ady TZIDON

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Solution: (Hide)

2*n - 3 .

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