if a man walks 6 miles at 4 miles an hour, how fast would he have to walk in the next 2.5 hours to average 6 mph

Question

Brain isnt working right, trying to get some help on this one. Should be a fairly simple problem but im drawing a blank. Thank you

Answer 1

Linda C's explanation is very good for solving the problem, but to understand how to set it up, I found the following webpage helpful:  http://www.purplemath.com/modules/distance.htm

Answer 2

Average is total miles divided by total hours.  So for how long did he walk already?  With that, we can solve this thing.

 

• (1 hr/4 miles)(6 miles)=1.5 hours
• Total miles = 6 miles (already walked) + x miles (unknown)
• Total time = 1.5 hours (already walked) + 2.5 hours (remaining time)
• 6 miles/hr = (6+x)/(1.5+2.5)
• 6=(6+x)/4
• 24=6+x
• 18=x

 

He needs to walk 18 miles in the next 2.5 hours, so 18/2.5=7.2 mph