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MathNet 2021 — Part 10 Question 14

Math Olympiad Vault · MathNet 2021 — Part 10

Question 14

What is the average number of pairs of consecutive integers in a randomly selected subset of $5$ distinct integers chosen from the set $\{1, 2, 3, \ldots, 30\}$? (For example, the set $\{1, 17, 18, 19, 30\}$ has $2$ pairs of consecutive integers.)
  1. $\frac{2}{3}$
  2. $\frac{29}{36}$
  3. $\frac{5}{6}$
  4. $\frac{29}{30}$
  5. $1$