Answer:
358800
Step-by-step explanation:
To create a four-letter password such that no letter are repeated and only lower cases are used;
For the first letter, we can choose any letter from A to Z = 26
We can choose any letter from A to Z except for the first letter for the second letter. = 25
We can choose any letter from A to Z except for the first & second letter for the third letter. = 24
We can choose any letter from A to Z except for the first, second & third letters for the fourth letter. = 23
SO;
No of ways in which 4-letter passwords are possible = 26 × 25 × 24 × 23
No of ways in which 4-letter passwords are possible = 358800