All 50 states as well as the District of Columbia and Puerto Rico, have distinct two-letter postal abbreviations. If a two-letter sequence of letters (such as CO or EE) is chosen at random, what is the probability that it is a postal abbreviation for one of the 50 states, the District of Columbia, or Puerto Rico? Express your answer as a common fraction.
Since you have 26 letters and repeats are allowed, then you have:
26^2 =676 combinations of 2 letters.
And, since you have 50+2 =52 postal abbreviation, then the probability is:
52 / 676 = 1/13 That a 2-letter combination would be a State's postal abbreviation.