Combining rates


Danielsville is 20 miles from Jim's home in Athens. He Drives 60 mph going to a meeting (he is almost late) but coming home the weather is bad and drives 30 mph. What is his combined speed for the time he is on the road?


A. Discuss why 45 mph is not correct.

Going to D'ville took 1/3 of an hour. Coming home took 2/3 of an hour. So the total 40 miles took one hour. The speed is 40 mph.


B. Use

d = r t

to verify and develop an understanding of how to combine rates. Elaboration.

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