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Solution: 2017 Winter Final - 18

Author: Michiel Smid

Question

You roll a fair red die and a fair blue die, independently of each other. Define the random variables
  • X = "the result of the red die",
  • Y = "the result of the blue die",
  • Z = $\min(X,Y)$.
What is $\Pr(Z = 2)$?
(a)
1/6
(b)
5/18
(c)
1/3
(d)
1/4

Solution

Let’s make a table and identify the minimums and when the occur

image

As we can see, the minimum of 2 occurs 9 times out of the total 36 possibilities

$ Pr(Z=2) = \frac{9}{36} = \frac{1}{4} $