Max of Two Dice
Goldman Sachs
You roll two 6-sided die, and get paid the maximum of the two face values. What's the fair price of this game?
Answer
Fair value of the game is the expected value we'd receive from playing it. We calculate this as the sum of possible maximum values (1-6) times their probabilites. 6 is the max if first die is 6 and second die is anything 1-5 (5 outcomes); if first die is anything 1-5 and second is 6 (5 outcomes); and if both are 6 (1 outcome). 11 in total: two symmetric cases where one die is the maximum value and other is strictly smaller, and one case where they both have the max value. Similarly, 5 is max in 9 cases; 4 in 7 cases and so on. The pattern is: n is the maximum of the two in 2n-1 ways. Each combination is equally likely, and there are 36 of them in total (6 possibilities for first die $\cdot$ 6 possibilities for the second).
Summing up all the outcomes multiplied with their probabilities, we get $EV = \sum_{n=1}^6 \frac{1}{36} \cdot (2n-1) = \frac{161}{36}$