SOLUTION: susan could run 16 miles at 4 mph and then run 8 miles at 2 mph. What should be her speed for 6 miles so that her overall average speed would be 3 mph? thanks!

Algebra ->  Average -> SOLUTION: susan could run 16 miles at 4 mph and then run 8 miles at 2 mph. What should be her speed for 6 miles so that her overall average speed would be 3 mph? thanks!      Log On


   

Question 1153205: susan could run 16 miles at 4 mph and then run 8 miles at 2 mph. What should be her speed for 6 miles so that her overall average speed would be 3 mph? thanks!
Answer by ikleyn(52797) About Me  (Show Source):
You can put this solution on YOUR website!
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susan could run 16 miles at 4 mph and then run 8 miles at 2 mph. What should be her speed for 6 highlight%28additional%29 miles
so that her overall average speed would be 3 mph? thanks!
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16 miles at 4 mph take  16%2F4 = 4 hours.


8 miles at 2 mph take  8%2F2 = 4 hours.


Let the time for additional 6 miles be  "t"  hours.


Then your equation is


    %2816%2B8%2B6%29%2F%284%2B4%2Bt%29 = 3  mph  (the desired average speed).


From the equation

    30%2F%288%2Bt%29 = 3,

    30 = 3*(8+t)

    30 = 24 + 3t

    30-24 = 3t,  

     6    = 3t

     t = 6/3 = 2 hours.


Hence, the last/additional 6 miles she should run at the average speed of  6%2F2 = 3 miles per hour.    ANSWER

Solved.