<pre>
ABCD
CABD
ACDB
DACB
BCDA
ACBD
ADCB
CDAB
DABC
BCAD
CADB
CDBA
CBAD
ABDC
ADBC
BDCA
DCBA
BACD
BADC
BDAC
CBDA
DBCA
DCAB
</pre>
Listed above are all of the permutations of the symbols &nbsp; '''A''', &nbsp; '''B''', &nbsp; '''C''', &nbsp; and &nbsp; '''D''', &nbsp; ''except'' &nbsp; for one permutation that's &nbsp; ''not'' &nbsp; listed.


;Task:
Find that missing permutation.


;Methods:
* Obvious method:
         enumerate all permutations of   '''A''',  '''B''',  '''C''',  and  '''D''',
         and then look for the missing permutation.

* alternate method:
         Hint:  if all permutations were shown above,  how many
         times would  '''A'''  appear in each position?
         What is the  ''parity''  of this number?

* another alternate method:
         Hint:  if you add up the letter values of each column,
         does a missing letter   '''A''',  '''B''',  '''C''',  and  '''D'''   from each
         column cause the total value for each column to be unique?


;Related task:
* &nbsp; [[Permutations]])
<br><br>
