Average Speed for the Round Trip

Jean drove 30 miles at a speed of 40 mph to see her cousin. In rush hour traffic returning home, Jean’s speed was only 20 mph. What was Jean’s average speed for the round trip?

Find the answers to these questions: How long did Jean spend driving to her cousin’s house? How long did Jean spend driving home? Remember the formula for average speed. If this value is different from the average of 40 mph and 20 mph, why is that so?