Combinatoricsmedium
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How many 5-element subsets of {1,2,3,...,12} contain at least one element from {1,2,3}?
How many 5-element subsets of {1,2,3,...,12} contain at least one element from {1,2,3}?
How many 5-element subsets of {1,2,3,...,12} contain at least one element from {1,2,3}?