Answer: 11,232,000
This result is a single number slightly over 11 million
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Work Shown:
Throughout all of this, order does matter (eg: ABC is different from BCA)
Focus on the letters for now
There are 26 letters total.
The first slot has 26 choices
The second slot has 25 choices (since we can't reuse whatever is in slot1)
The third slot has 24 choices
For just the letters only, we have 26*25*24 = 15600 permutations
Since we'll use this number later, let's call this M = 15600
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Now onto the numbers. There are 10 digits total
For slot 1 we have 10 choices
For slot 2 we have 9 choices
For slot 3 we have 8 choices
For just the numbers only, we have 10*9*8 = 720 permutations
Since we'll use this number later, let's call this N = 720
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Now multiply M and N
M*N = 15600*720 = 11,232,000
So we can generate 11,232,000 serial numbers