Answer
Mean: $7$
Standard deviation: $\sqrt{2}$
Work Step by Step
The discrete uniform distribution has the parameters:
$$a=5, b=9$$
Calculate the mean and the variance:
$$\mathbb{E}(X)=\frac{5+9}{2}=[7]$$
$$\operatorname{Var}(X)=\frac{(9-5+1)^{2}-1}{12}=2$$
$$\sigma=\sqrt{\operatorname{Var}(X)}=[\sqrt{2}]$$
