Thread: Calculating Average Rate

Is there a formula for calculating the average rate ?

The question is

If a tree grows 5 feet in n years , What was the average rate in inches per year at which the tree grew during those years ??

The answer is 60/n

I also got 60/n as the answer but i am not sure if my explanation for getting this answer is correct.
I got 60/n because the required value is average rate in inches per year . inches here is (12x5)/n = 60/n
Is this the correct reason for getting 60/n as the answer. Frankly i think this is a dumb question but it still appeared on GMAT.

Correct...dumb question for sure!