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ANSWER: 30 mph.

EXPLANATION: The fastest way to solve this is to assume a value for the distance traveled each way, say 60 miles. It would have taken an hour to go to the meeting and 3 hours to return, a total distance of 120 miles in 4 hours = 30 mph.

This can also be solved algebraically without assuming a value for the distance. Let d be the distance driven each way. The total distance is therefore 2d. Let t be the time the car travels 60 mph and T be the time the car travels 20 mph. Using the formula Speed × Time = Distance, we have: 60 × t = d and 20 × T = d. This gives t = d/60 and T = d/20.

Therefore:

• t + T = d/60 + d/20
• t + T = 80d/1200
• t + T = d/15

So the average speed (total distance / total time) is:

• Average Speed = 2d/(t + T)
• Average Speed = 2d/(d/15)
• Average Speed = 30 mph

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