Warm Up 1
(2.10.2014)
1) Simplify
2) Is the following sequence arithmetic or
geometric? Give the common ratio or
common difference.
9, 15, 21, 27, ….
Half-Life
Essential Question (2.10.2014)
How can we use exponential functions to
describe the half-life of a substance?
Review of Twizzler Activity
Key Points of Half-Life
B = ½ or 0.5
Base is ALWAYS ½ for half-life!
The amount will never reach 0!
If you are only taking away half each interval
you are still left with half!
Definition: Half-Life
The term half-life refers to the time it takes
for half of the atoms in a radioactive
substance to decay.
1)
For example, the half-life of carbon-11 is 20
minutes. Fill in the table to find the
amount of carbon-11 left after 3 half-life
cycles.
Number of
Half Life
Cycles
Amount
remaining
0
1
2
3
Worksheet problems
2)
The half-life of a radioactive substance is 2
days. There are currently 150 grams of
this substance.
a) Write an explicit equation.
b) How many grams will remain in 8 days?
3)
Hg-197 is used in kidney scans and it has a
half-life of 64.128 hours.
a)
Write the exponential decay function
for a 12-mg sample.
b)
Find the amount remaining after 72
hours.
Half Life Review Problems
Work in pairs to complete the 5 word
problems.
Coming up…
Homework – 5.10