I want to simplify this question and play with it.
We have 26 letters and 6 digits . Repetition is allowed.
I want to know how many combinations of 2 letters and 2 numbers that there are.
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there are 26^2=676 letter combinations
Now I know that in 26*1=26 of these the 2 letters are the same so the rest must be different.
That would be 26*25= 650 (Yes that works)
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there are 6^2=36 number combinations
6 have repetition and 30 do not
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Now when I put this together i can have
2 letters the same and 2 numbers the same 4!/(2!2!) = 3
26*6*3=468
2 letters the same and 2 numbers different 4!/2! = 12
26*30*12= 9360
2 letters diff and 2 numbers the same 4!/2!=12
26*25*6*12= 46800
2 letters diff and 2 numbers diff 4! = 24
26*25*6*5*24 = 78000
SO I think that the number of 4 tumbler codes would be 468+9360+46800+78000= 134,628
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NOW, I would like Sir CPhill and Chiurgeon Tud to comment on my solution to this simplified problem please.
Do you think that it is correct?