Question

Consider the game where two dice, die A and die B, are rolled. We say that die A wins, and write A > B, if the outcome of rolling A is larger than that of rolling B. If both rolls result in the same number it is a tie.
a. find the porbability of a tie
b. find the probabilty that die A wins

Answer 1

Answer:

a) The probability of a tie is the probability of getting the same outcome in both dice.

First, we roll die A and we get a given outcome. (here the probability is 1 because there is no restriction)

Now we need to roll die B and get the same outcome, so here we have only one possible outcome out of 6, then in this case the probability is 1/6

The joint probability (the product of the individual probabilities) is: P =  1*(1/6) = 1/6

b) We want to find the probability that die A wins.

Here we need to analyze each possible outcome for die A.

Let's define:

pₙ = probability of winning given that the outcome is n.

If the outcome is a 1, die A can only lose or tie, then here:

p₁ = 0

If the outcome is a 2, then die A only wins if die B rolls a 1, (1 outcome out of 6)

Then the probability of winning is:

p₂ = 1/6

If the outcome is a 3, then die A wins if die B rolls a 1 or a 2, here we have two possible outcomes out of 6.

p₃ = 2/6

We already can see the pattern, if the outcome is a 4, we get:

p₄ = 3/6

if the outcome is a 5:

p₅ = 4/6

if the outcome is a 6:

p₆ = 5/6

The total probability is the sum of all the joint probabilities:

For each roll in dice A, the probability is 1/6 (the probability of getting a given outcome)

Then the probability that die A wins is:

P = (1/6)*p₁ + (1/6)*p₂ + ... = (1/6)*(p₁ + p₂ + p₃ + p₄ + p₅ + p₆)

P = (1/6)*(0 + 1/6 + 2/6 + 3/6 + 4/6 + 5/6)

P = (1/6)*(15/6) = 0.4167