1. Exponential Growth occurs when a quantity
increases by a fixed percent each time period.
Models for exponential growth:
a is the initial amount
r or k is the percent of increase in decimal form
t is the time

2. Exponential Decay occurs when a quantity
decreases by a fixed percent each time period.
Models for exponential decay:
a is the initial amount
r or k is the percent of decrease in decimal form
t is the time

17. The half-life of Sodium-22 is 2.6 years.
What is the value of k for Sodium-22?

18. A geologist examining a meteorite estimates that it
contains only about 10% as much Sodium-22 as it
would have contained when it reached the surface of
the Earth. How long ago did the meteorite reach the
surface of the Earth?
Answer: It was
formed about 9
years ago.