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 letter A?
Answers:  A) 16,250  B) 16,500  C) 16,750  D) 17,000  E) 17,250
The number of two-letter codes is  25*25= 
<gadget id="calculator"> 25*25</gadget>
<output>625</output>
625.   The number of three-letter codes is 25*25*25=15,625.   The total number of codes is 625+15,625=16,250.   The answer is 16,250.
<result>A</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 letter A?