Statistics And Probability Question 587

Question: Let S be a set containing n elements and we select 2 subsets A and B of S at random then the probability that $ A\cup B=S $ and $ A\cap B=\varphi $ is

[Orissa JEE 2005]

Options:

A) $ 2^{n} $

B) $ n^{2} $

C) 1/n

D) $ 1/2^{n} $

Show Answer

Answer:

Correct Answer: D

Solution:

  •         Ways of selection two subset of  $ A={{(2^{n})}^{2}} $             Ways of selection  $ A\cup B $  and  $ A\cap B $  are  $ 2^{n} $                  \Required probability  $ =\frac{\text{favourable cases}}{\text{total cases}}=\frac{2^{n}}{{{(2^{n})}^{2}}}=\frac{1}{2^{n}} $ .