Logic puzzle: Which octopus is telling the truth? King Octopus has servants with six, seven, or eight legs. The servants with seven legs always lie, but the servants with either six or eight legs always tell the truth. 
One day, four servants met.
The blue one says, “Altogether, we have 28 legs.”
The green one says, “Altogether, we have 27 legs.”
The yellow one says, “Altogether, we have 26 legs.”
The red one says, “Altogether, we have 25 legs.”
What is the colour of the servant who tells the truth?

The green one is telling the truth. 
We know this because all of them gave different numbers which means that three out of the four servants are lying because only 1 total number of legs can be correct. So, since all 7 legged servants are liars, and we know 3 are lying, we multiply 7 * 3 and get 21. So 3 out of the 4 servants there have a total of 21 legs. The only options are 28(blue),27(green),26(yellow), and 25(red) so we know the red one is lying because the difference between 21 and 25 is 4 and there are no 4 legged servants. There are also no 5 legged servants so the yellow one is lying too. And the difference between 21 and 28 is 7, that would mean that they were all liars which isn't true. So Green is the only one left. The green is telling the truth and has 6 legs. 
