7.5E: Exercises - Applications of Exponential and Logarithmic Functions

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PROBLEM SET: APPLICATIONS OF EXPONENTIAL AND LOGARITHMIC FUNCTIONS

An investment’s value is rising at the rate of 5% per year. The initial value of the investment is $20,000 in 2016. Write the function that gives the value of the investment as a function of time $t$ in years after 2016. Find the value of the investment in 2028 When will the value be $30,000?	The population of a city is increasing at the rate of 2.3% per year, since the year 2000. Its population in 2010 was 137,000 people. Find the population of the city in the year 2000.
The value of a piece of industrial equipment depreciates after it is purchased. Suppose that the depreciation follows an exponential decay model. The value of the equipment at the end of 8 years is $30,000 and its value has been decreasing at the rate of 7.5% per year. Find the initial value of the equipment when it was purchased.	An investment has been losing money. Its value has been decreasing at the rate of 3.2% per year. The initial value of the investment was $75,000 in 2010. Write the function that gives the value of the investment as a function of time $t$ in years after 2010. If the investment’s value continues to decrease at this rate, find the value of the investment in 2020.
A social media site has 275 members initially. The number of members has been increasing exponentially according to the function $y = 275e^{0.21t}$, where $t$ is the number of months since the site’s initial launch. How many months does it take until the site has 5000 members? State answer to the nearest tenth of a month (1 decimal place).	A city has a population of 62000 people in the year 2000. Due to high unemployment, the city’s population has been decreasing at the rate of 2% per year. Using this model, find the population of this city in 2016.
A city has a population of 87,000 people in the year 2000. The city’s population has been increasing at the rate of 1.5% per year. How many years does it take until the population reaches 100,000 people?	An investment of $50,000 is in increasing in value at the rate of 6.3% per year. How many years does it take until the investment is worth $70,000?
A city has a population of 50,000 people in the year 2000. The city’s population increases at a constant percentage rate. Fifteen years later, in 2015, the population of this city was 70,000. Find the annual percentage growth rate.	200 mg of a medication is administered to a patient. After 3 hours, only 100 mg remains in the bloodstream. Using an exponential decay model, find the hourly decay rate.
An investment is losing money at a constant percentage rate per year. The investment was initially worth $25,000 but is worth only $20,000 after 4 years. Find the percentage rate at which the investment is losing value each year (that is, find the annual decay rate).	Using the information in question 11, how many years does it take until the investment is worth only half of its initial value?

For question 13:

if the function is given in the form $y = ae^{kt}$, rewrite it in the form $y = ab^t$.
if the function is given in the form $y = ab^t$ , rewrite it in the form $y = ae^{kt}$.

13a. $y=7900e^{0.472t}$. Write in the form $y=ab^t$	13b. $y=4567(0.67^t)$. Write in the form $y=ae^{kt}$
13c. $y=18720(1.47^t)$. Write in the form $y=ae^{kt}$	13d. $y=1200e^{-0.078t}$. Write in the form $y=ab^t$

13a. \(y=7900e^{0.472t}\). Write in the form \(y=ab^t\)	13b. \(y=4567(0.67^t)\). Write in the form \(y=ae^{kt}\)
13c. \(y=18720(1.47^t)\). Write in the form \(y=ae^{kt}\)	13d. \(y=1200e^{-0.078t}\). Write in the form \(y=ab^t\)

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