This is the question of jee 2010 , paper 2 maths... Q)Let S = {1, 2, 3, 4}. The total number of unordered pairs of disjoint subsets of S is equal to (A) 25 (B) 34 (C) 42 (D) 41 Sol. (D) the solution I got at a site was Total number of unordered pairs of disjoint subsets = (3^4 + 1)/2 = 41 Please tell how did they reach at this solution?..

Dear shubhi,

There is a generalised formula: 3^n+1/2 so you can use this formula....

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