What is the average rate of change of water depth in the lock over the first two minutes ?

Question

When a pleasure boat enters a small lock, there are 120 inches of water (depth) in the lock. Two minutes later after the lock begins draining, there are 102 inches of water in the lock.

 

Answer 1

The average rate of change is the slope of the line connecting the two points, (0 minutes, 120 feet) and (2 minutes, 102 feet):

 

slope = (102-120)/(2-0) = -18/2 = -9 feet per minute