Mihir N.

### Problem 53

[T] A vehicle has a 20 -gal tank and gets 15 mpg. The number of miles $N$ that can be driven depends on the amount of gas $x$ in the tank.
a. Write a formula that models this situation.
b. Determine the number of miles the vehicle can travel on (i) a full tank of gas and (ii) 3$/ 4$ of a tank
of gas.
c. Determine the domain and range of the function.
d. Determine how many times the driver had to stop for gas if she has driven a total of 578 $\mathrm{mi}$ .

Linh V.

### Problem 54

[T] The volume $V$ of a sphere depends on the length of its radius as $V=(4 / 3) \pi r^{3}$ . Because Earth is not a perfect sphere, we can use the mean radius when measuring from the center to its surface. The mean radius is the average distance from the physical center to the surface, based on a large number of samples. Find the volume of Earth with mean radius $6.371 \times 10^{6} \mathrm{m} .$

Mihir N.

### Problem 55

[T] A certain bacterium grows in culture in a circular region. The radius of the circle, measured in centimeters, is given by $r(t)=6-\left[5 /\left(t^{2}+1\right)\right], \quad$ where $t$ is time
measured in hours since a circle of a 1 -cm radius of the bacterium was put into the culture.
a. Express the area of the bacteria as a function of time.
b. Find the exact and approximate area of the bacterial culture in 3 hours.
c. Express the circumference of the bacteria as a function of time.
d. Find the exact and approximate circumference of the bacteria in 3 hours.

Linh V.

### Problem 56

[T] An American tourist visits Paris and must convert U.S. dollars to Euros, which can be done using the function $E(x)=0.79 x,$ where $x$ is the number of U.S. dollars and $E(x)$ is the equivalent number of Euros. Since conversion rates fluctuate, when the tourist returns to the United States 2 weeks later, the conversion from Euros to U.S. dollars is $D(x)=1.245 x,$ where $x$ is the number of Euros and
$D(x)$ is the equivalent number of U.S. dollars.
a. Find the composite function that converts directly from U.S. dollars to U.S. dollars via Euros. Did this tourist lose value in the conversion process?
b. Use (a) to determine how many U.S. dollars the tourist would get back at the end of her trip if she
converted an extra $\$ 200$when she arrived in Paris. Mihir N. Numerade Educator ### Problem 57 [T] The manager at a skateboard shop pays his workers a monthly salary$S$of$\$750$ plus a commission of $\$ 8.50$for each skateboard they sell. a. Write a function$y=S(x)$that models a worker's monthly salary based on the number of skateboards$x$he or she sells. b. Find the approximate monthly salary when a worker sells$25,40,$or 55 skateboards. c. Use the INTERSECT feature on a graphing calculator to determine the number of skateboards that must be sold for a worker to earn a monthly income of$\$1400$ . (Hint: Find the intersection of the
function and the line $y=1400 .$ )

Linh V.
[T] Use a graphing calculator to graph the half-circle $y=\sqrt{25-(x-4)^{2}} .$ Then, use the INTERCEPT feature to find the value of both the $x$ - and $y$ -intercepts.