Intermediate Algebra – Student Workbook – Second Edition 2013

Lesson 3b – More Exponential Functions
Practice Problems
10. For each of the following,
Determine if it is Exponential Growth or Exponential Decay.
Write the equation the appropriately models the scenario.
If it is growth, determine the doubling time.
If it is decay, determine the half life.
These are word problems, so make sure your final answer is in a complete sentence.
a) BoringBob buys a piece of gold that has a value of $1000. His investment grows at a rate
of 5% per year. How long until his investment doubles?
b) Twidles has 50 rabbits. He usually keeps the separated, but one day he leaves them all
free in the back yard (with lots of food and water) and heads off for a 7 day vacation.
The rabbits do what rabbits do and the population starts growing at a rate of 10% a day.
Will Twidles have 100 rabbits when he gets back?
c) Jeffta went to a doctor and found out that he had 80 pounds of body fat and needed to
lose 40 of that. He goes on a healthy diet and finds that he is losing 2% of his body fat a
week. How long will it take Jeffta to lose the 40 pounds?
d) In 1975, the cost of a Bean Burro from Taco Bell costs 25 cents. Inflation has averaged
about 3% a year since then. In what year did it reach 50 cents. In what year should it
cost $1.00? Let t = the number of years since 1975 (i.e. t = 0 for 1975, t = 1 for 1976
and so on).
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