Car A drives west at a speed of 30 km/hr starting from a McDonald's. 20 minutes later, Car B starts driving west at a speed of 35 km/hr from a location 50 kilometers directly north of the same McDonald's. How quickly (i.e., with respect to time) is the distance between Cars A and B changing 20 minutes after Car B started driving?

You can solve this either by using a single function of time () or by applying the chain rule to multiple related length quantities that each vary with respect to The second solution method will be more similar to the solution methods employed for the remainder of the discussion.