Question
A is a set containing n elements. A subset P1 is chosen, and A is reconstructed by replacing the elements of P1. The same process is repeated for subsets P1, P2, … , Pm, with m > 1. The Number of ways of choosing P1, P2, …, Pm so that P1 P2 … Pm= A is -
- (2m – 1)mn
- m+nCm
- (2n – 1)m
- None of these
The correct answer is: None of these
Let A = {a1, a2,…..an}.
For each ai (1 i n), either ai Pj or ai Pj (1 j m) . Thus, there are 2m choices in which ai (1 j n) may belong to the Pj s.
Also there is exactly one choice, viz., ai Pj for j = 1, 2, …, m, for which ai P1 P2 ... Pm.
Therefore, ai P1 P2 …. Pm in (2m – 1) ways . Since there are n elements in the set A, the number of ways of constructing subsets
P1, P2, ….. , Pm is (2m – 1)n
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