Exponential Functions Percent Increase and Decrease

A student invests $500 for x years in a savings account that earns 4% interest per year. No further deposits or withdrawals are made during this time. Write an function f(x) to represent the amount of money earned after x years.

• f(x) = 500 (.60)^x

• f(x) = 500 (.96)^x

• f(x) = 500 (1.04)^x

• f(x) = 500 (1.4)^x

Which of the following functions shows an initial amount of $15 and an increase of 35% each year?

• y = 15(1.035)^x

• y = 15(1.35)^x

• y = 15(0.35)^x

• y = 15(0.65)^x

A bird species is decreasing at a rate of 2% each year. If there are currently 150,000 of these birds, which function would determine the number of birds B, after n years?

• B = 15000(0.02)ⁿ

• B = 15000(1.02)ⁿ

• B = 15000(0.98)ⁿ

• B = 15000(0.80)ⁿ

There were 417 cell phones sold at an electronics store in January. Since then, cell phone sales at this store have increased at a rate of 3.75% per month. At this rate of growth, which function can be used to determine the monthly cell phone sales x months after January?

• f(x) = 417(3.75)^x

• f(x) = 417(0.0375)^x

• f(x) = 417(1.0375)^x

• f(x) = 417(1.375)^x

An antibiotic is introduced into a colony of 12,000 bacteria during a laboratory experiment. The colony is decreasing by 15% per minute. Which function can be used to model the number of bacteria in the colony after x minutes?

• f(x) = 12000(1.15)^x

• f(x) = 12000(0.15)^x

• f(x) = 12000(0.85)^x

• f(x) = 12000(1.85)^x

The number of student athletes at a local high school is 300 and increasing at a rate of 8% per year. How man student athletes will there be after 5 years?

• 441

• 197

• 440

• 198

An investment of $8,200 loses value at a rate of 2% per year. To the nearest cent, what will be the value of the investment after 9 years?

• $8,531.28

• $6,836.73

• $3.28

• $7875.30

The population of a town is decreasing at a rate of 1% per year. In 2000 there were 1300 people. What will the population be in 2008?

• 0

• 332,800

• 1,408

• 1,200

The equation below models the amount of students in a school after x years. Find the rate it is changing after x years.

• 23% increase

• 23% decrease

• 77% increase

• 77% decrease

An economist predicts that the number of employees with a certain company will increase by 50% each year. There are 600 employees now. According to the economist’s prediction, how many employees will be with the company exactly 3 years from now?

• 2,025

• 38

• 64,800

• 24,000