Subsets in Order

Problem

Let $I = \{1, 2, 3, 4, 5\}$ . Choose two nonempty subsets $A, B$ of $I$ such that the smallest element of $B$ is greater than the largest element of $A$ . How many such choices are there?

Answer

Solution

Difficulty	6/10
Topics	combinatorics, Counting, Casework

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