Official papers

Official 2020 Paper 2 · Q19

Paper 2Geometry

Nine people are sitting in the squares of a 3 by 3 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.) Diagram for question 19 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?

smallest largest
A 1 4
B 2 4
C 2 5
D 3 4
E 3 5
F 4 4
G 4 5
H 5 5
ABCDEFGH

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