Let . Find the number of unordered triples that satisfy
Solution
To find the number of unordered triples that satisfy where , we need to consider the following steps:
1. **Counting the ways to assign each element to subsets , , and :**
Each element in can be in any of the subsets , , or , or in any combination of these subsets. There are possible ways to assign each element to the subsets , , and (since each element can either be in or out of each subset).
2. Excluding the empty assignment:
Out of these 8 possibilities, one possibility is that the element is not in any of the subsets , , or . This is not allowed since must cover all elements of . Therefore, we have valid ways to assign each element to the subsets.
3. Calculating the total number of assignments:
Since each of the elements in can be assigned to the subsets in 7 different ways, the total number of ways to assign all elements is .
4. Considering unordered triples:
The problem asks for unordered triples . However, since the assignment of elements to subsets is inherently ordered, we do not need to further adjust for ordering.
Thus, the total number of unordered triples that satisfy is .
The final answer is