Answer: \(\dfrac{4}{29}\)
Step-by-step explanation:
We know that the formula to find the conditional probability of A given that B is given by :-
\(P(A|B)=\dfrac{P(A\cap B)}{P(B)}\)
Let A be the event that students own mobile phones of Brand X and B be the event that students own mobile phones of Brand Y.
Then , \(P(A)=\dfrac{420}{1000}\)
\(P(B)=\dfrac{580}{1000}\)
\(P(A|B)=\dfrac{80}{1000}\)
Then , the required probability will be:-
\(P(A|B)=\dfrac{\dfrac{80}{1000}}{\dfrac{580}{1000}}\\\\\\\Rightarrow P(A|B)=\dfrac{4}{29}\)