Question 636456: If a computer code contains 2 letters and 3 numbers and none can repeat, how many combinations are possible?
I am thinking:
26*25*24...*1*25 PLUS 9*8*7...*1*8*7. Would that be correct for the formula?
Thank you!
Jama
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! Your formula does not sound right. I cannot figure out how you derived it. My logic gives me different answers. (Disclaimer: I have been wrong at times)
I see two possible interpretations of the problem:
 a computer code/password is made up of two letters together, followed by 3 numbers,
like  ,
you have 26 choices for the first character.
For each of those 26 choices, you have 25 choices for the second character.
That gives you 26*25 choices for the two beginning characters (letters).
For each of those 26*25 choices, you have 10 choices for the third character.
That results in 26*25*10 choices for the first three characters.
For each of those 26*25*10 choices, you have 9 choices for the fourth character.
You end up with 26*25*10*9 choices for the first four characters.
For each of those 26*25*10*9 choices, you have 8 choices for the fifth character.
That gives you  choices overall.
However, the letters and numbers could be scrambled into any order,
like  , or  ,
there are more possibilities.
In that case, the 26*25 two letter codes, would be  two-letter sets,
because codes AB and BA use the same set {A, B}.
Similarly, the 10*9*8 three-digit codes represent  three three-digit sets.
Then, you would have  different sets made of 2 letters and three digits.
Each set could be re-arranged  different ways, giving you
 different codes.
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