Final answer:
The student's question contained a typo but likely refers to finding the number of elements in the union of two sets. Assuming they meant n(A ∪ B), by applying the principle of inclusion-exclusion, the answer is calculated to be 12.
Step-by-step explanation:
The question seems to be based on a typo since n (A B) is not a standard mathematical notation when referring to sets or numbers of elements in sets. However, it is possible that the student might be asking about the principle of inclusion-exclusion or maybe the union or intersection of sets. One common interpretation of the question could be finding n(A ∩ B), which represents the number of elements in the intersection of sets A and B.
Assuming that n (A ∩ B) = 36 represents the number of elements in the intersection of sets A and B, and we want to find n(A ∪ B), which is the number of elements in the union of sets A and B, we can use the principle of inclusion-exclusion:
n(A ∪ B) = n(A) + n(B) - n(A ∩ B)
Substituting the given values:
n(A ∪ B) = 20 + 28 - 36 = 12
Therefore, the number of elements in the union of sets A and B is 12.