Q.

Let S={w1,w2,…} be the sample space associated to a random experiment. Let P(wn)=P(wn-1)2,n≥2. Let A={2k+3l:k,l∈ℕ} and B={wn:n∈A}. Then P(B) is equal to                 [2023]

1 116  
2 364  
3 332  
4 132  

Ans.

(2)

Given S={w1,w2,…} be the sample space associated to a random experiment. If  

P(Wn)=P(Wn-1)2,n≥2

and let A={2k+3l:k,l∈N} and B={wn:n∈A}.

First of all, let P(w1)=λ. Then P(w2)=λ2

P(wn)=λ2 n-1

As 
∑k=1∞P(wk)=1⇒λ1-12=1⇒λ=12

So P(Wn)=12n

A={2k+3l:k,l∈N}={5,7,8,9,10,…}

B={wn:n∈A}

B={w5,w7,w8,w9,w10,w11,…}

A=N-{1,2,3,4,6}

P(B)=1-[P(w1)+P(w2)+P(w3)+P(w4)+P(w6)]

=1-[12+14+18+116+164]=1-32+16+8+4+164=364