# Probabilities : Marginals

A bag contains r balls, of which 2 are red and r - 2 are black. We draw a ball at random, we write down its color, and we put it to one side (not back in the bag). We repeat the procedure r times.

Let X be the number of draws needed to obtain a red ball, and let Y be the number of draws needed to obtain a second red ball.

a. Find the probability law of the vector (X,Y) , and find its marginals.

b. Evaluate Cov(X,Y) .

https://brainmass.com/math/probability/probabilities-marginals-18556

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A bag contains balls, of which 2 are red and are black. We draw a ball at random, we write down its colour, and we put it to one side (not back in the bag). We repeat the procedure r times.

Let X be the number of draws needed to obtain a red ...

#### Solution Summary

Probailities are calculated using appropriate tables and calculations. The solution is detailed.