SOLUTION: You drive on Interstate 10 from San Antonio to Houston, half the time at 50 km/h and the other half at 82 km/h. On the way back you travel half the distance at 50 km/h and the othe

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: You drive on Interstate 10 from San Antonio to Houston, half the time at 50 km/h and the other half at 82 km/h. On the way back you travel half the distance at 50 km/h and the othe      Log On

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Question 753567: You drive on Interstate 10 from San Antonio to Houston, half the time at 50 km/h and the other half at 82 km/h. On the way back you travel half the distance at 50 km/h and the other half at 82 km/h.

What is your average speed for the entire trip?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Average speed is always ( total distance traveled ) / ( total time )
Let +d+ = total distance traveled
Let +2t+ = total time
--------------------
Half the time is spent traveling at +50+ km/hr
+d%5B1%5D+=+50t+
Half the time is spent traveling at +82+ km/hr
+d%5B2%5D+=+82t+
-------------
+d+=+d%5B1%5D+%2B+d%5B2%5D+
+d+=+50t+%2B+82t+
-----------------
The average speed is
+d+%2F+%28+2t+%29+=+%28+50t+%2B+82t+%29+%2F+%28+2t+%29+
The t's cancel
Average speed = 132 / 2
Average speed = 66 km/hr