A drug is carried into an organ of volume V $cm^3$ by a liquid that enters the organ at the rate of a $\mathrm{cm}^{3} / \mathrm{sec}$ and leaves it at the rate of b $\mathrm{cm}^{3} / \mathrm{sec}$. The concentration of the drug in the liquid entering the organ is c $\mathrm{g} / \mathrm{cm}^{3}$. If the concentration of the drug in the organ at time t is increasing at the rate of $x^{\prime}(t)=\frac{1}{V}\left(a c-b x_{0}\right) e^{-b t v}$ $\mathrm{g} / \mathrm{cm}^{3} / \mathrm{sec}$ and the concentration of the drug in the organ initially is $x_{0} \mathrm{g} / \mathrm{cm}^{3}$, show that the concentration of the drug in the organ at time t is given by $x(t)=\frac{a c}{b}+\left(x_{0}-\frac{a c}{b}\right) e^{-b c v}$

Use the data in the table, which shows the average annual salaries (both in thousands of dollars) for librarians and postsecondary library science teachers in the United States for 12 years.

$$\begin{matrix} \text{Librarians, x} & \text{Library science teachers, y}\\ \text{49.1} & \text{56.6}\\ \text{50.9} & \text{57.6}\\ \text{52.9} & \text{59.7}\\ \text{54.7} & \text{61.6}\\ \text{55.7} & \text{64.3}\\ \text{56.4} & \text{67.0}\\ \text{57.0} & \text{70.0}\\ \text{57.2} & \text{70.8}\\ \text{57.6} & \text{73.3}\\ \text{58.1} & \text{72.4}\\ \text{58.9} & \text{73.0}\\ \text{59.9} & \text{72.3}\\ \end{matrix}$$

Construct a scatter plot for the data. Do the data appear to have a positive linear correlation, a negative linear correlation, or no linear correlation? Explain.

Find the density function of $Y=e^{Z}$, where $Z \sim N\left(\mu, \sigma^{2}\right)$. This is called the lognormal density, since log Y is normally distributed.

In the children's game rock, paper, scissors, two players simultaneously extend one hand in the form of a fist (rock), a flat palm (paper), or two fingers extended (scissors). If they both make the same choice, the game is a tie. Otherwise, rock beats scissors (because rock can crush scissors), scissors beats paper (because scissors can cut paper), and paper beats rock (because paper can cover rock). Whoever wins gains one point; in the case of a tie, no one gains any points. (a) Find the optimum strategy for each player and the value of the game. (b) In hindsight, how could you have guessed the answer to part (a) without doing any work?

Suppose that the probability of living to be older than 70 is .6 and the probability of living to be older than 80 is .2. If a person reaches her 70th birthday, what is the probability that she will celebrate her 80th?

Show that a group of order 24 with no element of order 6 is isomorphic to $S_{4}$.

The number of saltwater crocodiles in a certain area of northern Australia is given by $P(t)=\frac{300 e^{-0.024 t}}{5 e^{-0.024 t}+1}$ a. How many crocodiles were in the population initially? b. Show that $\lim _{t \rightarrow \infty} P(t)=0$. c. Plot the graph of P in the viewing window $[0,200] \times [0,70]$.

Find an invertible matrix P and a matrix C of the form

$$\left[\begin{array}{rr} a & -b \\ b & a \end{array}\right]$$

such that the given matrix has the form $A=P C P^{-1}$.

$$\left[\begin{array}{rr} 4 & -2 \\ 1 & 6 \end{array}\right]$$

Use logarithmic differentiation to find the derivative of the function. $y=\left(x^{2}+1\right)^{x}$

Prove the following two identities both algebraically and by interpreting their meaning combinatorially. a.

$$\left(\begin{array}{l} n \\ r \end{array}\right)=\left(\begin{array}{l} n \\ n-r \end{array}\right)$$

b.

$$\left(\begin{array}{l} n \\ r \end{array}\right)=\left(\begin{array}{l} n-1 \\ r-1 \end{array}\right)+\left(\begin{array}{c} n-1 \\ r \end{array}\right)$$

A sample of sulfur weighing 0.210 g was dissolved in 17.8 g of carbon disulfide,$\mathrm{CS}_{2}\left(\mathrm{K}_{\mathrm{b}}=2.43^{\circ} \mathrm{C} / \mathrm{m}\right)$. If the boiling point elevation was 0.107 $^{\circ} \mathrm{C}$, what is the formula of a sulfur molecule in carbon disulfide?

Find the upper and lower central series for $A_{4}$ and $S_{4}$.

Find the absolute maximum value and the absolute minimum value, if any, of the function. $h(t)=8 t-\frac{1}{t^{2}}$ on [1, 3]

Let $f(x)=x^{2}+a x+b$. Determine the constants a and b such that f has a relative minimum at x=2 and the relative minimum value is 7.