# Which octopus spoke the truth?

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It is known that octopuses with 7 legs always lie, while those with 6 legs and those with 8 legs always tell the truth. One night, four octopuses met:

Black — 'We have 28 legs.'
Green — 'We have 27 legs.'
Yellow — 'We have 26 legs.'
Red — 'We have 25 legs.'

Who spoke the truth?

posted Aug 17, 2015

+1 vote

27 legs
Of the 4 octopuses at least 3 lie. These three have 7 legs each = 21 legs. If the 4th octopus also has 7 legs, the total is 28 legs, but all octopuses must lie. This black octopus says 28 legs, so this is not the case. If the 4th octopus has 8 legs, the total is 29 legs, but no octopus says that, meaning all must lie. This can also not be true. If the 4th octopus has 6 legs, the total is 27 legs. The green octopus is then the only one who speaks the truth.

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