how many two-letter codes can be formed using the letters A,B,C, and D? repeated letters are allowed.

Question

 This question is about forming codes.

Answer 1

it says repeat letters are allowed but it doesn't say code ab is different than ba so there are 10 unique codes not 16

Answer 2

You have two places and any letter can be at any place, thus, you have

N=4²=16 codes.

 

AA

AB

AC

AD

BB

BA

BC

BD

CA

CB

CC

CD

DA

DB

DC

DD