SOLUTION: A car travels at 40 mph for the first half and for the second half at 60 mph, what is the average speed for the entire journey

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Question 819800: A car travels at 40 mph for the first half and for the second half at 60 mph, what is the average speed for the entire journey
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Average speed always = ( total distance ) / ( total time )
Let +2d+ = total distance
Let +t%5B1%5D+ = time for 1st part of trip
Let +t%5B2%5D+ = time for 2nd part of trip
-------------------
For 1st part of trip:
+d+=+40t%5B1%5D+
+t%5B1%5D+=+d%2F40+
-----------
For 2nd part:
+d+=+60t%5B2%5D+
+t%5B2%5D+=+d%2F60+
---------------
Average speed:
+2d+%2F+%28+d%2F40+%2B+d%2F60+%29+
+%28+2+%2F+%28+1%2F40+%2B+1%2F60+%29+%29%2A%28+d%2Fd+%29+
Multiply top and bottom by +120+
+%28+2%2A120+%29+%2F+%28+3+%2B+2+%29+
+240+%2F+5+=+48+
The average speed for the entire journey is
48 mi/hr