In one of his books, Ted Sorenson, Special Counsel to President John F. Kennedy, presents an intimate

Question:

In one of his books, Ted Sorenson, Special Counsel to President John F. Kennedy, presents an intimate biography of the extraordinary man. According to Sorenson, Kennedy "read every fiftieth letter of the thirty thousand coming weekly to the White House." What type of sampling design was Kennedy using in this case? Explain your answer