<PRE><B>Question 1147968</B>
24
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The workout:

Along the perimeter:  2*9 + 2*5 = 28  but subtract 4 because each corner is counted twice, leaving 24.

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More generally...

To see the pattern, imagine the room has only 4 tiles in a 2x2 arrangment: the perimeter is 2*2+2*2 = 8, and subtracting 4 leaves 4.

For a 3x3 configuration: 2*3+2*3 = 12, 12-4 = 8  (clearly correct as only the center tile does not touch a wall or door, and 3*3-1 = 8).

etc.


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