Brain-Teaser 485

From The Sunday Times, 13th September 1970 [link]

Delphi has three computers, in order to confuse the faithful. The 1969 one always gives a true answer; the 1960 one always gives an untrue answer; the 1965 is quite unpredictable.

Professor Binary, who is visiting the shrine, fed to each computer in turn the question: “What is the date of the largest computer?”

The first computer replied “1969”; the second replied “Not 1960”; and Binary, who could see the size, though not the date, of the computers as they replied, had no need to study the third computer’s reply, since he now knew the answer to his question.

What is the date of the largest computer?

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