## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$25$
A,B,C,D and E are 5 distinct objects from which we should make 2-letter codes. This implies, n=5. Since repetition is allowed, the number of two letter codes is: $= n(n) \\= 5(5) \\= 25$