A program generates random strings with $5$ letters which can be any of $a,g,j,o,x,y,z$ with repetitions allowed
How many different strings have two or more identical letters ?
I don’t understand the concept of two or more identical letters can someone explain?
HINT:
To count the number of strings having more identical letters subtract the number of strings having all unique letters from the number all the possible strings.
To find all possible strings think how many different characters you may choose as the first letter, the second and so on.
To find all strings having unique letters (no two identical characters) find the number of different ways to choose $5$ characters out of your given alphabet and figure out in how many ways you can arrange these.
Hope this helped