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jmc

counting and probability senior

Problem

Ben rolls two fair six-sided dice. What is the expected value of the larger of the two numbers rolled? Express your answer as a fraction. (If the two numbers are the same, we take that number to be the "larger" number.)
Solution
There are 36 possible outcomes for the two dice. Of these, there is 1 where both dice roll a six, 5 where the first die rolls a six and the other rolls something less than a six, and 5 more where the second die rolls a six and the first die rolls something less than a six. So, there are a total of ways the larger number rolled can be a six. Similarly, there are ways the larger number rolled can be a five, ways the larger number rolled can be a four, ways the larger number rolled can be a three, ways the larger number rolled can be a two, and way the larger number rolled can be a one. The expected value of the larger number is
Final answer
\frac{161}{36}