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, B, or C? Select
A) 10,494	B) 11,585	C) 12,696	D) 13,787	E) 14,898
The number of two-letter codes is  23*23= 
<gadget id="calculator"> 23*23</gadget>
<output>529</output>
529.   The number of three-letter codes is 23*23*23=12,167.   The total number of codes is 529+12,167=12,696.   The answer is 12,696.
<result>C</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, B, or C?