Question 1100893
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The condition of this problems IS NOT COMPLETED.


If you have the letters in the first and second position ONLY, and the digits in the last positions ONLY, 

it is one set, and Alan correctly determined the number of elements in this set.



If, in opposite, the letters can be placed in any two of available 4 positions, it will be TOTALLY different set 
with the TOTALLY DIFFERENT number of elements.


Since the condition does not determine this VITALLY IMPORTANT information, <U>your post is not a formulation of a Math problem AT ALL</U>.