The following table lists the probability distribution for cash prizes in a lottery conducted at Lawson's Department Store.
$$\begin{array}{|rc|}\hline \text { Prize (\$) } & \text { Probability } \\\hline 0 & .45 \\10 & .30 \\100 & .20 \\500 & .05 \\\hline\end{array}$$
If you buy a single ticket, what is the probability that you win:
a. Exactly $\$ 100 ?$
b. At least $\$ 10 ?$
c. No more than $\$ 100 ?$
d. Compute the mean, variance, and standard deviation of this distribution.