Answer
$10.5$
Work Step by Step
1. When one die is rolled, the expected value of the number of dots is 3.5.
2. In Exercise 20, the mean number of dots was found for rolling two dice
has been found as $7$, which is twice of $3.5$
3. For the case that three dice are rolled, by using simple reasoning and
data extrapolation, the mean number should be $3\times3.5=10.5$
