### Instruction: 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.### Response: To solve this problem, I need to compare the number of possible two-letter sequences with the number of valid postal abbreviations.
There are 26 letters in the alphabet, so the number of possible two-letter sequences is 26 times 26, or 676.
The number of valid postal abbreviations is 50 plus 2, or 52.
Therefore, the probability of choosing a valid postal abbreviation at random is 52 out of 676, or 13 out of 169.