posted by Jassie .
How many codes consisting of a letter followed by 3 digits can be made if no digit can be used more than once?
This assumes the letter "O" is allowed. Often it is not, because of confusion with zero. IT also assumes case of the letters is indifferent. If case masters, then A and a will be different, so you double the number of codes available.
can you tell me how you got 9 and 8?
I get it 26 alphabets.