Combinatoricshard
0:00.0
How many 6-element subsets of {1, 2, ..., 20} contain exactly 2 elements from {1, 2, ..., 5}?
How many 6-element subsets of {1, 2, ..., 20} contain exactly 2 elements from {1, 2, ..., 5}?
How many 6-element subsets of {1, 2, ..., 20} contain exactly 2 elements from {1, 2, ..., 5}?