Exponential Functions Depreciate

Most automobiles depreciate as they get older. Suppose an automobile that originally costs $14,000 depreciates by 20% of its value every year. 
What exponential equation can we create to model this situation?

• y=14000(.20)^x
• y=14000(.80)^x
• y=14000(1+.20)^x
• y=14000(1+.80)^x

Most automobiles depreciate as they get older. Suppose an automobile that originally costs $20,000 depreciates by 28% of its value every year.  What is the half-life of this automobile?

• 2 years
• 3 years
• 1/2 years
• 2.11 years

Most automobiles depreciate as they get older. Suppose an automobile that originally costs $14,000 depreciates by 20% of its value every year. 
What is the value of this automobile after 5 years?

• $264,539.52
• $4.48
• $4,587.52
• $34,836.48

A sculpture is increasing in value at a rate of 9% per year, and its value in 2000 was $1500. Write an exponential growth function to model this situation.

• f(t)=1500(1.09)^t
• f(t)=1500(0.09)^t
• f(t)=2000(0.09)^t
• f(t)=1500(9)^t

Suppose a culture of bacteria begins with 5000 cells and dies by 30% each year. Write an equation that represents this situation.

• y=5000(0.7)^x
• y=30(5000)^x
• y=5000(1.3)^x
• y=5000x^x

Write an equation that models the following situation:
Samantha's hair was known to grow very rapidly. It began at a length of 6 in and grew at a rate of 14% a week.

• y=6(0.14)^x
• y=6(1+14)^x
• y=6(1.14)^x
• y=6(0.86)^x

The half-life of strontium-90 is 25 years. How much strontium-90 will remain after 100 years if the initial amount is 4.0 g?

• 3.0g
• 0.25mg
• 0.3g
• 0.25g