Subject identification numbers in a certain scientific research project consist of two letters followed by two...

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Subject identification numbers in a certain scientific research project consist of two letters followed by two digits and then two more letters. Assume repetitions are not allowed within any of the three groups, but letters in the first group of two may occur also in the last group of two. How many distinct identification numbers are possible? There are distinct identification numbers possible. Subject identification numbers in a certain scientific research project consist of two letters followed by two digits and then two more letters. Assume repetitions are not allowed within any of the three groups, but letters in the first group of two may occur also in the last group of two. How many distinct identification numbers are possible? There are distinct identification numbers possible.