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Miles drives the same path to and from work. If he averages 50 miles per hour on the way to work and 75 miles per hour on the way from work, what is the average speed of his entire commute?

 Jun 12, 2021
 #1
avatar+121004 
+2

Avg speed  = 

 

2* product of speeds  /  sum of speeds    =

 

(2 * 50 * 75)   /( 50 + 75)  =

 

7500  / 125  =

 

60  mph           

 

[   NOT      (50 + 75)  / 2  =  125 / 2  =     62.5  mph  as many think  !!!    ]

 

 

cool cool cool 

 Jun 12, 2021
 #2
avatar+33689 
+1

Time to work =  distance / rate = d/50

Time from work =  d/75

 

total distance = 2d

 

total distance / total time =  average rate

 

2d / (d/50 + d/75) =   2 / ( 1/50 + 1/75) = 2 / (3/150 + 2/150) =  2/ (5/150) = 300/5 = 60 m/hr     ( as Chris found via different method !)

 Jun 12, 2021

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