Here's a tricky one to finish off our week. You drive to the store at 20 mph and return home using the same route at 30 mph. Discounting the time spent at the store and assuming no traffic, what was your average speed?
Here's a tricky one to finish off our week. You drive to the store at 20 mph and return home using the same route at 30 mph. Discounting the time spent at the store and assuming no traffic, what was your average speed?
Permalink: http://problemotd.com/problem/average-speed/
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Comments:
Heroka - 10 years, 5 months ago
24 mph.
When we set distance at 1 (because it's irrelevant), it takes 1/20 hour to drive to the store and 1/30 hour to drive back. Thus, total time spent driving is 1/20 + 1/30 = 5/60 = 1/12 hour. Total distance is 2. As speed is distance / time, the mean speed is 2/(1/12) = 24.
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