SOLUTION: A jogger runs from her home to the shop at an average speed of 12 km/h. When she gets there she finds that the shop is closed. She walks back home at a constant speed of 4 km/h. wh

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Question 1050086: A jogger runs from her home to the shop at an average speed of 12 km/h. When she gets there she finds that the shop is closed. She walks back home at a constant speed of 4 km/h. what is the average speed?
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 spent traveling ]
Let +d+ = one-way distance between home and shop
----------------
Time spent jogging:
+t%5B1%5D+=+d+%2F+12+ hrs
Time spent walking:
+t%5B2%5D+=+d+%2F+4+ hrs
----------------------
Average speed =
+%282d%29+%2F+%28%28+t%5B1%5D+%2B+t%5B2%5D+%29%29+
+%282d%29+%2F+%28%28+d%2F12+%2B+d%2F4+%29%29+
+%28+d%2Fd+%29%2A%28+2+%2F+%28+1%2F12+%2B+1%2F4+%29%29+
+2+%2F+%28%28+1%2F12+%2B+3%2F12+%29%29+
+2+%2F+%28+4%2F12+%29+
+2+%2F+%28+1%2F3+%29+=+6+
The average speed is 6 km/hr