By inspecting the curve, the gradient function (f') itself is decreasing (starts off with high gradient then lowers down near 0), so we can say f is increasing at a decreasing rate.
Example values,
x = 0.01, y' = 100
x = 0.2, y' = 5
x = 5, y' = 0.2
x = 100, y' = 0.01
Since y' is clearly...