Interview Question: Primal Instinct Again

Sample Question #72 (mathematical brainteaser)

(I was asked this at a Goldman Sachs interview a few years ago. Luckily I had already known the answer. Smile )

Can the average of two consecutive prime numbers ever be a prime? If so, provide an example.

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One Response to Interview Question: Primal Instinct Again

  1. Brett says:

    Let the two consecutive prime numbers be a and b, where a < b. If c is their average, we know a < c < b, because both a>0 and b>0. Now, if c were also a prime, what would be wrong with the premise of the question? 

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