SOLUTION: A man walks six miles at four miles per hour. At what speed would he need to travel during the next two and a half hours to have an average speed of six miles an hour during the e

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Question 512601: A man walks six miles at four miles per hour. At what speed would he need to travel during the next two and a half hours to have an average speed of six miles an hour during the entire trip?
Found 2 solutions by solver91311, josmiceli:
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


Since he has already been walking for 1 and 1/2 hours (distance divided by rate equals time, so 6 divided by 4 = 1.5), the entire trip for which he wants to average 6 miles per hour is 4 hours long (2.5 plus 1.5). 6 miles per hour times 4 hours is 24 miles. He has already travelled 6 miles, so he needs to travel 18 more miles (24 minus 6) in 2.5 hours. 18 divided by 2.5.

He better find a bicycle.

John

My calculator said it, I believe it, that settles it
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Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Average speed is ( total distance ) / ( total time )
For the 1st 6 miles
+6+=+4%2At+
+t+=+1.5+ hrs
Let +s+ = speed for last +2.5+ hrs
--------------
Average speed = +6+ mi/hr
Total distance = +6+%2B+2.5s+
+%28+6+%2B+2.5s+%29+%2F+%28+1.5+%2B+2.5+%29+=+6+
+%28+6+%2B+2.5s+%29+%2F+4+=+6+
+6+%2B+2.5s+=+24+
+2.5s+=+18+
+s+=+7.2+
He would have to travel at 7.2 mi/hr