Exponential Functions from Word Problems

You have inherited land that was purchased for $30,000 in 1960. The value of the land increased by approximately 5% per year. What is the approximate value of the land in the year 2011?

• $344,022
• $31,500
• $15,000
• $28,500

An adult takes 400 mg of ibuprofen. Each hour, the amount of ibuprofen in the person’s system decreases by about 29%.

What is the multiplier for this problem?

Hint: Multiplier is another term for decay factor.

• 1.29

• .71

• .29

• 1.71

You drink a beverage with 120 mg of caffeine. Each hour, the caffeine in your system decreases by about 12%. How long until you have 10mg of caffeine? 

• 19 to 20 hours
• 10 to 20 hours
• 15 to 16 hours
• 5 to 6 hours

The foundation of your house has about 1,200 termites. The termites grow at a rate of about 2.4% per day. How long until the number of termites doubles?

• 29 to 30 days

• 23 to 24 days

• 15 to 16 days

• 19 to 20 days

Is this exponential growth or decay?

• Growth because a=1
• Decay because b=0.5
• Growth because there is no a
• Neither because a=0

Pick the equation that is exponential decay

• y=2000(0.88)
• y=0.5(1.88)
• y=-4x
• y= -7+10x

Pick the equation that is exponential growth

• y=2(0.5)^x
• y = 0.5(2)^x
• y = .5x - 2
• y = 2x + .5 

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

You buy a new computer for $2100. The computer decreases by 50% annually. How much is it worth after 2 years.

• 225

• 325

• 425

• 525