Octagon Counter

Eight 1 1 -by- 2 \sqrt{2} rectangles are formed by drawing a rectangle intersecting another at 4 5 45^{\circ} angle at a vertex and an opposite edge. Each of 49 separated regions represents a number of 1 1 -by- 2 \sqrt{2} rectangles it is contained in.

What is the sum of all numbers?

Clarification: Here is the example of the number in a certain region in the starting rectangle formation.


The answer is 200.

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2 solutions

Zico Quintina
Jul 11, 2018

First, it took me a few moments to even figure out which rectangles were being used to create the figure, so here's an image with one of the rectangles in green; if you imagine rotating it in 4 5 45^\circ increments about the green central point, you can see all eight rectangles.

filler {\color{#FFFFFF} \text{filler}}

filler filler {\color{#FFFFFF} \text{filler}} \\ {\color{#FFFFFF} \text{filler}}

The three images below show regions with value 1, 2 and 3; the red rectangles are the only ones containing the shaded regions.

filler {\color{#FFFFFF} \text{filler}}

filler filler {\color{#FFFFFF} \text{filler}} \\ {\color{#FFFFFF} \text{filler}}

The next three images show regions with value 5, 6 and 7; the blue rectangles are the only ones NOT containing the shaded regions.

filler {\color{#FFFFFF} \text{filler}}

filler filler {\color{#FFFFFF} \text{filler}} \\ {\color{#FFFFFF} \text{filler}}

Clearly, the central region is contained by all eight rectangles. Finally, here's an image showing all the region values:

filler {\color{#FFFFFF} \text{filler}}

filler filler {\color{#FFFFFF} \text{filler}} \\ {\color{#FFFFFF} \text{filler}}

There are eight regions each with values of 1, 2, 3, 5, 6, and 7, and one region with value 8; so the total value of all regions is

8 ( 1 + 2 + 3 + 5 + 6 + 7 ) + 8 = 200 8 \ (1 + 2 + 3 + 5 + 6 + 7) + 8 = \boxed{200}

Jon Haussmann
Jul 17, 2018

Each 1 × 2 1 \times \sqrt{2} rectangle contains 25 regions. Therefore, the sum of the region values is 8 25 = 200 8 \cdot 25 = 200 .

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