1. Warm Up: Mr. Dodd currently has 21 koi in his backyard pond
Warm Up: Mr. Dodd currently has 21 koi in his backyard pond. If the population is growing at a rate of 15% per year, how many koi will be in the pond in 4 years?

2. 8.2 Exponential Decay
Objective: Use exponential decay functions to model real life situations

3. General form: or

4. Calculating Decay Factors:
Decrease of 5%
Decrease of 50%
Decrease of 19.8%
Decrease of 100%
Decrease of 200%

5. Ex. 1: You buy a car for $24,000. The value, y, of the car decreases by 16% each year.
Write an exponential decay function to model the value of your car.
Approximate the value after 2 years.
How long will it take for the car’s value to be less than $12,000?

6. Ex. 2: The half-life of a hazardous substance is measured as the time that it takes for half the amount of the substance to decay. The half-life of the pesticide DDT is 15 years, and a 100g sample is improperly disposed of.
Write an exponential decay function to model the scenario.
b. What does x represent?
c. How much of the pesticide will still be present at the disposal site in 75 years?