Verified answer

Figure out the total amount of potential results. Assuming that letters can be repeated and all letters can be used. You do this by multiplying the amount of potential results in any one space (26) by itself the number of times that there is the potential for a number to occur (10).

There is 141,167,095,653,376 potential combinations of letters.

To find the likelihood of A or B, you have 2 results out of 26, or a thirteenth. Divide the number above by 13. You get 10,859,007,357,952.

26^10 -- 24^10 ANSWER