TMUA 2020 Paper 2 Question 19
P2·Logic & Quantifiers, Sets & Counting·7.5Official · 2020 · Q19
truth-tellers-liarscase-analysisgrid-puzzle
Nine people are sitting in the squares of a grid, one in each square, as shown. Two people are called neighbours if they are sitting in squares that share a side. (People in diagonally adjacent squares, which only have a point in common, are not called neighbours.)
Each of the nine people in the grid is either a truth-teller who always tells the truth, or a liar who always lies. Every person in the grid says: 'My neighbours are all liars'.Given only this information, what are the smallest number and the largest number of people who could be telling the truth?
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