In Exercises $11$ through $14$, find the appropriate value of $b$ for the given probability, assuming that the random variable $Z$ has a standard normal distribution.

$$P(Z \leqq b)=0.8413$$

In Exercises $11$ through $14$, the joint probability density function $f(x, y)$ for two continuous random variables $X$ and $Y$ is given. In each case, find the expected values $E(X)$ and $E(Y)$.

In Exercises $1$ through $14$, determine whether the given function is a probability density function.

$$f(x, y)= \begin{cases}2 e^{-(6 y+x / 3)} & \text { for } x \geq 0, y \geq 0 \\ 0 & \text { otherwise }\end{cases}$$

In Exercises $5$ through $10$, find the indicated probability assuming that the random variable $Z$ has a standard normal distribution.

$$P(-1.20 \leq Z \leq 4.26)$$

In each of Exercises $1$ through $10$, determine whether the given random variable $X$ is discrete or continuous.

$X$ measures the speed of a randomly selected car passing a police speed trap.