A man drives at an average speed of 60 mph going to a meeting, but coming home, the weather is bad and
he drives at an average speed of only 20 mph. What is his average speed for the time he is on the road?

**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

Do you have a

suggestion for this puzzle (e.g. something that should
be mentioned/clarified in the question or solution, bug, typo, etc.)?