A certain stock exchange designates each stock with a 1 , 2 or 3-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?
26 for the first letter 26^2 for the second 26^3 for the third.
To elim the need for calculations just realize that the units digit will be 6 and there are three 6's.
So the units digit will be 8.