document.write( "Question 1132911: How many different ways are there to place four different digits from 1 to 4 inside the four square cells of a 2-by-2 grid (one digit per cell) such that for every pair of digits that are 1 apart (such as 2 and 3), their square cells share a side?
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Algebra.Com's Answer #750061 by ikleyn(52847) $\"\"$ $\"About$

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document.write( "You can place the digit \"1\" into any of 4 cells.\r\n" );
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document.write( "Then you have 2 and only 2 possible adjacent cells to place the digit \"2\" there.\r\n" );
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document.write( "After that, you have one and only one free adjacent cell to place the digit \"3\" there.\r\n" );
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document.write( "Finally, you have only 1 remaining cell to put the digit there \"4\" without any other choice.\r\n" );
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document.write( "Fortunately, this last cell is adjacent to \"3\", so all requirements are satisfied.\r\n" );
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document.write( "So, the full number of ways is 4*2 = 8 different placements.\r\n" );
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