If the number ofproper subsets of a set A is 31, find the number of elements of A.
Let the number of elements of set A = n.
Therefore, total number of proper subset = 2n - 1
⇒2n - 1 = 31 [Given, number of proper subset = 31]
⇒2n = 32
⇒2n = 25
⇒n = 5
Hence,the number of elements of A is 5.