Average rate of change

From point (a,f(a))=(0,0) to point (b,f(b))=(4,200). Average rate of change is slope of secant line,
which is Δy/Δx = (ƒ(b)-ƒ(a)) / (b-a) = (200-0)/(4-0) = 50

Average rate of change over the interval [-2,8]: from (-2,2.4) to (8,-1.6) is slope of the secant line connecting them,
which is (-1.6-2.4)/(8--2) = -4/10 = -.4
Average rate of change over the interval [2,6]: from (2,-1.6) to (6,-2.4) is slope of the secant line connecting them,
which is (-1.6--2.4)/(2-6) = .8/-4 = -.2
Average rate of change over the interval [0,10]: from (0,0) to (10,0) is slope of the secant line connecting them,
which is (0-0)/(10-0) = 0/10 = 0