Question

Suppose p(x1) = .75 and p(y2 | x1) = .40. what is the joint probability of x1 and y2?

Answer 1

By definition of conditional probability,

$\mathbb P(Y_2\mid X_1)=\dfrac{\mathbb P(Y_2\cap X_1)}{\mathbb P(X_1)}$

so

$\mathbb P(Y_2\cap X_1)=0.40\times0.75=0.3$