aerage rate of change is just the slope from the endpoints of teh interval
ie [tex]averagerateofchange=slope=\frac{f(5)-f(1)}{5-1}[/tex]
assuming you mean [tex]f(x)=480(0.3)^x[/tex]
evalaute f(5) and f(1)
f(5)=480(0.3)^5=1.1664
f(1)=480(0.3)^1=144
average rate of change=(1.1664-144)/(5-1)=-35.7084
the average rate of change of the function on the interval x=1 to x=5 is -35.7084
