Application of Decay Functions

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

The value of a car is $15,000 and depreciates at a rate of 8% per year. What is the decay factor?

• ^.08

• ^1.08

• .92

• 8

The value of a car purchased for $20,000 decreases at a rate of 12% per year. What will be the value of the car after 3 years?

• $12,800.00

• $13,629.44

• $17,600.00

• $28,098.56

A sailboat that costs $5,950 decreases in value by 11% per year. How much will the boat be worth after 6 years?

• $5,884.00

• $5,178.97

• $2,992.96

• $2,957.04

A medicine is applied to a burn on a patient's arm. The area of the burn in square centimeters decreases exponentially and is shown in the graph.

What is the area of the burn after 7 weeks? Round to three decimal places.

A radioactive substance decays by 10% every hour. If there are initially 400 grams of the substance, how much will be left after 3 hours?

• 291.6

• 0.4

• 532.4

• 400

Every hour an antibiotic is left in your body, the amount present DECREASES by 5%. If you started with 34mg of medicine in your body how much is left after 5 hours?

• about 26mg

• about 43mg

• about 20mg

• about 15mg

Does the following equation show growth or decay?
y=10,000*(0.76)^x

• Growth 

• Decay

Your shiny new boat cost $7650.  The depreciation for your boat is 14% per year. Estimate the value of your vehicle in 3 years. What is the equation that models this problem?

• y= 7650(.14)³

• y= 7650(.86)³

• y= 7650(1+.86/1)^3*1

The value of a car is $15,000 and depreciates at a rate of 8% per year. What is the exponential equation?

• y=8(15,000)^x

• y=15,000(1.08)^x

• y=15,000(0.92)^x

• y=15,000(0.08)^x