If the number of ways in which four distinct balls can be put into two identical boxes such that no box remains empty is equal to k , then k is

Step-by-step solution

Every ball has two options ⇒       4   balls can be put in 2 4 ways. Arrangement among themselves is 2 ! So, total ways = 1 2 ! × 2 4 =   2 3 But, above count also includes the one case in which all the balls are put in one box, ⇒   required number of ways k =   2 3 - 1 = 7