ABCD
CABD
ACDB
DACB
BCDA
ACBD
ADCB
CDAB
DABC
BCAD
CADB
CDBA
CBAD
ABDC
ADBC
BDCA
DCBA
BACD
BADC
BDAC
CBDA
DBCA
DCAB
Listed above are all of the permutations of the symbols   '''A''',   '''B''',   '''C''',   and   '''D''',   ''except''   for one permutation that's   ''not''   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: *   [[Permutations]])