The problem says:
We have strings formed by two letters, followed by two digits and then followed by three letters. In each group repetitions are not allowed, but the last group of three letters can contain up to one of those used in the first group. If the number of letters available is 12 how many different strings can be formed?
Well, my solution is this:
Considering that the first letter is repeated, the letters and digits in order: (12*11)*(10*9)*(12*10*9)=12830400
Considering that the second letter is repeated, the letters and digits in order: (12*11)*(10*9)*(11*10*9)=11761200
So, by the sum of the two cases: 12830400+11761200=24591600
The result of my solution is not in the list of choices, but is close to A.
I noticed that A can be obtained with: 11761200+11761200=23522400, wich i dont understand why that would be correct, this is like saying 12830400+12830400 is ok too...
I think A is wrong, but the others are wrong too, so maybe I am doing something wrong.