SOLUTION: If Joe drives to work at 30mph and drives home at 50mph. What is his average speed for the round trip? (round to the nearest decimal, it is not 40).

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Question 326529: If Joe drives to work at 30mph and drives home at 50mph. What is his average speed for the round trip? (round to the nearest decimal, it is not 40).
Found 2 solutions by galactus, solver91311:
Answer by galactus(183) About Me  (Show Source):
You can put this solution on YOUR website!
The total distance is 2d. Because it is d there and d back.
The total time is d%2F30%2Bd%2F50
Average speed is then 2d%2F%28d%2F30%2Bd%2F50%29=37.5
The d's cancel.

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


The distance to work is the same as the distance coming home, so for the trip to work:



and for the trip home



The average round trip speed is then 2 times the one-way distance divided by the sum of the elapsed times:



Substituting from the first two relationships:



A little algebra to simplify the compound fraction:



Verification of the previous step left as an exercise for the student.




John