4. Suppose that we have 60, 000, 000 families in the United states. Random variable X is constructed in the following way: I choose a family uniformly at random (each family is chosen with probability...

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Extracted text: 4. Suppose that we have 60, 000, 000 families in the United states. Random variable X is constructed in the following way: I choose a family uniformly at random (each family is chosen with probability 1/60, 000, 000), and count the number of children in that family. Suppose that E(X) = 2.4. I construct random variable Y in the following way: Pick a child at random in the USA, and count the number of siblings of that child. It turns out the E(Y) = 1.55. Calculate var(X).