SOLUTION: A truck driver travels a certain distance at 60 miles per hour and returns over the same road at 40 miles per hour. What is her average rate for the round trip? I know it is a d

Question 242908: A truck driver travels a certain distance at 60 miles per hour and returns over the same road at 40 miles per hour. What is her average rate for the round trip?
I know it is a d=rt but I don't know where to begin. Can Please help by explaining thoroughly.
Answer by Edwin McCravy(20054) (Show Source): You can put this solution on YOUR website!
A truck driver travels a certain distance at 60 miles per hour and returns over the same road at 40 miles per hour. What is her average rate for the round trip?
I know it is a d=rt but I don't know where to begin. Can Please help by explaining thoroughly.



Notice that you are NOT given the distance, but the distance will not
matter, because the answer is independent of the distance.  However
we have to let distance be a variable d anyway.

Make this chart:

             Distance      Rate       Time
Going
Returning
---------------------------------------------
Totals                     XXXX 

Fill in the distances, which are both d

             Distance      Rate       Time
Going           d            
Returning       d          
----------------------------------------------
Totals                     XXXX                     

Fill in their total 2d

             Distance      Rate       Time
Going           d           
Returning       d          
----------------------------------------------
Totals         2d          XXXX     

Fill in the rates, which are 60 and 40


             Distance      Rate       Time
Going           d           60      
Returning       d           40        
----------------------------------------------
Totals         2d          XXXX     

Use the formula  to fill
in the times:

             Distance      Rate       Time 
Going           d           60        d/60 
Returning       d           40        d/40
----------------------------------------------
Totals         2d          XXXX       

Total up the times

             Distance      Rate       Time
Going           d           60        d/60 
Returning       d           40        d/40
----------------------------------------------
Totals         2d          XXXX     d/60 + d/40  


Now to calculate the average rate

Average rate =  

To simplify that complex fraction, multiply top and bottom by 120:











See how the d's canceled?  That shows it didn't matter what the
distance d was, and there is no way of finding out because it
could be any number of miles.



miles per hour.

Edwin

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