jmc

Each outcome of rolling a 6-sided die has probability $\frac{1}{6}$, and the possible outcomes are 1, 2, 3, 4, 5, and 6. So the expected value is $$\frac{1}{6}(1)+\frac{1}{6}(2)+\frac{1}{6}(3)+\frac{1}{6}(4)+\frac{1}{6}(5)+\frac{1}{6}(6)=\frac{21}{6}=\boxed{3.5}.$$