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2 problems match “counting pairs”. Clear

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1. Matches in a round-robin group ●○○○○ 10 ptsA group has four teams, and each team plays every other team in the group exactly once. How many matches are played in the group?
2. Removing an element to raise probability ●●○○○ 20 ptsTwo different numbers are randomly selected from the set $S = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11\}$. The probability that their sum is 12 would be greater if the number $n$ had first been removed from $S$. What is the value of $n$?