A certain stock exchange designates each stock with a two-letter or three-letter code, where each letter is selected from the 26 letters of the alphabet. If the letters may be repeated and if the same letters used in a different order constitute a different code, how many different stocks is it possible to uniquely designate with these codes without using the letters A or Z?  Choose the correct choice from the following.
A) 13.8  B) 14,400  C) 15,000  D) 15,600  E) 16,200
The number of two-letter codes is  24*24= 
<gadget id="calculator"> 24*24</gadget>
<output>576</output>
576.   The number of three-letter codes is 24*24*24=13,824.   The total number of codes is 576+13,824=14,400.   The answer is 14,400.
<result>B</result>
A certain stock exchange designates each stock with a two-letter or three-letter code, where each letter is selected from the 26 letters of the alphabet. If the letters may be repeated and if the same letters used in a different order constitute a different code, how many different stocks is it possible to uniquely designate with these codes without using the letters A or Z?