Sarah M.

asked • 10/08/14

Average Speed

A boy riding his bicycle travels at 10 miles per hour for 3 hours. He stops to rest for one hour and then continues his ride. For the next hour he rides at 20 miles per hour. During his ride, what was the riders average speed for the five hour period?

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Ralph L. answered • 10/08/14

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10mph*(3 hours) + 20mph*(1 hour) = 50 miles
 
total time is 3 hours + 1 hour + 1 hour = 5 hours
 
50 miles/5 hours
 
10 mph
 
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Arthur D.

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Ralph,
I would not count the one hour he rested. What if he stayed at a motel overnight for 12 hours ? His time would then be 16 hours and his rate would be 50 miles/16 hours=3 2/3 mph. To me it doesn't make sense to count his time resting, or rather, not bicycling. I would say 50 miles/4 hours=12.5 mph for the average speed. To me what is misleading is the question asked: "average speed for the five hour period". He wasn't traveling for the entire five hours, only four of those hours. To me it's sort of a trick question to see if the student can determine what information is relevant to solving the problem and what information is not. What do you think ? or any other tutors
who want to comment.
 
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10/08/14

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