Higher Average Rolls Lower

Suppose I have two fair dice A \text{A} and B . \text{B}. Each can have any number of faces, and a positive integer is written on each face. Is it possible that A \text{A} has a greater average roll value while B \text{B} has a greater chance of rolling higher on an individual roll?

No Yes

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1 solution

The answer is Yes \boxed{\text{Yes}} . As an example using fair 6-sided dice, (fair meaning that each side has an equal chance of being on top), let dice A A have face numbers 1 , 1 , 1 , 1 , 1 , 8 1,1,1,1,1,8 and dice B B have face numbers 2 , 2 , 2 , 2 , 2 , 2 2,2,2,2,2,2 . Then the average roll value for dice A A is 1 + 1 + 1 + 1 + 1 + 8 6 = 13 6 \dfrac{1 + 1 + 1 + 1 + 1 + 8}{6} = \dfrac{13}{6} , while the average roll value for dice B B is 2 2 . Yet of the 6 × 6 = 36 6 \times 6 = 36 outcomes from rolling both dice simultaneously, for only 6 6 of those outcomes will dice A A have a higher value than dice B B , i.e., dice B B will have a 5 / 6 5/6 chance of having a higher individual roll.

An example where all side numbers are distinct is 1 , 2 , 3 , 4 , 5 , 37 1,2,3,4,5,37 for dice A A and 6 , 7 , 8 , 9 , 10 , 11 6,7,8,9,10,11 for dice B B .

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