Population Growth and Decline The graph shows the population P in a small industrial city from 1950 to 2000. The variable x represents the number of years since 1950. (a) What was the average rate of change of P between x = 20 and x = 40? (b) Interpret the value of the average rate of change that you found in part (a). P (thousands) + 50 40 30 20 10 0 10 20 30 40 50 * (yr) a): b) AVERAGE RATE OF CHANGE The average rate of change of the function y = f(x) between x = a and x = b is change in y f(b) - f(a) average rate of change = change in x b - a