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Random variable is a variable of which values depend on outcomes of a random phenomenonFormally, it is a measurable function defined on a probabiltiy
1\. Sum rule (Marginal probability)$$P(X = x_i) = \\sum_j^m P(X = x_i, Y = y_j)$$$$p(X = x_i) = \\int_j p(X = x_i, Y = y_j) dy$$2\. Product rule$$P(X