Question

If number of proper subsets of a set is 63, then the number of elements in the set is .........​

Answer 1

Answer:

If A has cardinality n, then the number of subsets is 2n and the number of proper subsets is 2n−1, because the only set we have to "throw out" is A itself in order to get all the proper subsets. A set A is a subset of a set B if every element of A is also an element of B.