If A is a subset of B and B is a subset of C, then cardinality of A ∪ B ∪ C is equal to

The cardinality of A ∪ B ∪ C is equal to the cardinality of C. This is because, given that A is a subset of B and B is a subset of C, all elements of A and B are also elements of C. Therefore, the union of A, B, and C does not add any new elements beyond those already in C. Hence, the number of elements in A ∪ B ∪ C is the same as the number of elements in C.