Answer:
there is not enough information to solve
Step-by-step explanation:
You need two ordered pairs to calculate the average rate of change.
Let's say the value of the function at n = 1 is a, and the value of the function at n = 3 is b, then the average rate of change from n = 1 to n = 3 is
(b - a)/(3 - 1) = (b - a)/2
