Answer:
Explanation:
Total letters available on the keyboard = 26
Doubling this amount to account for both upper and lower case letters.
Therefore, Total characters (Upper + Lower Case) = 52 characters
Total numbers on keyboard (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) = 10 characters
Underscore = 1 character
Thus, Total allowed characters = 52 + 10 + 1 = 63
This is a problem of the permutation as order of the characters results in a different name.
Our file name should be of atleast 3 and smaller than 7 (i.e. 6) characters
Therefore, total possible permutations can be obtained by subtraction permutation of 2 characters from the permutations of 6 characters.