Slipt checkboard

Consider the decomposition of a checkerboard in p p rectangles that do not intersect and umple the following conditions:

  1. Each rectangle has the same quantity of white and black squares.

  2. There is not two rectangle with the same quatity of squares.

Find the maximum value of p p


The answer is 7.

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2 solutions

Ivan Koswara
Feb 19, 2015

Assuming checkerboard is the standard 8x8 chessboard. (Checkers have two common sizes, 8x8 and 10x10.)

Condition 1 requires the rectangles to have an even area. On the other hand, any rectangle (along the gridlines) with even area will satisfy condition 1, so we can replace condition 1 with "each rectangle has an even area".

Suppose there are n n rectangles. The minimum area covered is 2 + 4 + 6 + + 2 n = n ( n + 1 ) 2+4+6+\ldots+2n = n(n+1) , due to condition 2 requiring all rectangles to have different areas. Thus we need n ( n + 1 ) 64 n(n+1) \le 64 , or n 7 n \le 7 . So the theoretical maximum is 7 \boxed{7} rectangles. This is achievable in many ways; here's one that I think of:

Paola Ramírez
Feb 14, 2015

We have that 32 1 + 2 + 3 + 4... p = p ( p + 1 ) 2 32\geq 1+2+3+4...p=\frac{p(p+1)}{2} where 64 p ( p + 1 ) 64\geq p(p+1) so p 7 p\leq7 .

\therefore all the posible descomposition with p = 7 p=7 are:

1 + 2 + 3 + 4 + 5 + 6 + 11 = 32 1+2+3+4+5+6+11=32 this is not possible by 11 11

1 + 2 + 3 + 4 + 5 + 7 + 10 = 32 1+2+3+4+5+7+10=32

1 + 2 + 3 + 4 + 5 + 8 + 9 = 32 1+2+3+4+5+8+9=32

1 + 2 + 3 + 4 + 6 + 7 + 9 = 32 1+2+3+4+6+7+9=32

1 + 2 + 3 + 5 + 6 + 9 + 8 = 32 1+2+3+5+6+9+8=32

The last four can be form \therefore the maximum p = 7 \boxed{p=7}

For completeness, can you provide an actual decomposition of the checkerboard to show that it can indeed be formed? Thanks!

Calvin Lin Staff - 6 years, 3 months ago

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