Question 21
A biologist has a set of cages in a $4\times4$ array. He wants to put one mouse (black or white) into each cage in such a way that each mouse has at least one neighbour of each colour (neighbouring cages share a common wall).
The black mice are more expensive, so he wants to use as few of them as possible. What is the smallest number of black mice that he needs?
The black mice are more expensive, so he wants to use as few of them as possible. What is the smallest number of black mice that he needs?