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).

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) (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
Average speed is then
The d's cancel.
Answer by solver91311(24713) (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

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