[tex]f(t)=100(0.8)^t[/tex]
The equation is in the format
[tex]f(t)=ab^t[/tex]
where a is the initial value (when t=0), b is the rate of change between terms, and t is the amount of time.
Our initial value is 100. We find the rate of change by first finding the percent of change:
amount of change/original amount
= 20/100 = 0.2
This is a percent decrease, so we will subtract it from 1:
1-0.2 = 0.8
This goes in for b.
