Exponential decay is when an original amount is reduced by a consistent rate over a period of time, is generally expressed in percent change.
Exponential functions are represented by:
[tex]\begin{gathered} y=a(1-b)^x \\ \text{where,} \\ a=\text{original amount} \\ (1-b)=\text{decay factor or percent rate of decrease} \\ x=\text{represents time} \end{gathered}[/tex]Then, a percent rate of decrease of 5% is equal to 0.05 in decimal form.
Therefore, the function that has this decay factor is:
[tex]f(x)=3(0.05)^x[/tex]