Question 24
We need to remove several unit squares from a $6\times6$ grid such that there does not exist any area that have 6 unit squares which are connected via common sides. What is the minimum number of unit squares that we must remove?
For example, in the lower left figure below, the shaded area is an example of an area that have 6 unit squares which are connected together; while the lower right figure shows an example of a grid which does not have any 6 unit squares that are connected together left.
For example, in the lower left figure below, the shaded area is an example of an area that have 6 unit squares which are connected together; while the lower right figure shows an example of a grid which does not have any 6 unit squares that are connected together left.