find average rate of change for this function f(x)=2x from x[1]=0 to x[2]=5

Average rate of Change of a function is (ƒ(x_{2}) - ƒ(x_{1}))/(x_{2} - x_{1})

-----> (2 · 5 - 2 · 0)/(5 - 0) = 10/5 = 2

In case of direct variation (y=kx) the average rate of change is always "k"