Question 818285:  [ A car travels 180 km at 70 km/h and returns to the initial departure point at 60 km/h. Calculate average speed of the car. ] 
 Answer by TimothyLamb(4379)      (Show Source): 
You can  put this solution on YOUR website! s = d / t 
t = d / s 
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outbound: 
ta = d / s 
ta = 180/70 
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return: 
tb = d / s 
tb = 180/60 
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total time: 
ta + tb = (180/70) + (180/60) 
ta + tb = 5.5414286 hours 
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average speed: 
s = d / t 
s = (2)(180) / (ta + tb) 
s = (360) / (5.5414286) 
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s = 64.615 kph 
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