<PRE><B>Question 553281</B>
If he travels 20  miles at 50 mi/h, then time = D/r = 20/50 = .4 hr .


If he travels 20 miles at 40 mi/hr, then time = D/r= 20/40 = .5 hr .


The AVERAGE SPEED = (TOTAL DISTANCE)/(TOTAL TIME) = 40 miles/.9 hr = 44.44 mi/hr.


I think maybe your box method may not be appropriate for this one!


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