<PRE><B>Question 1201574</B>

a motorist travels from A to B at an average speed of 20km per hour
distance =10km

time = 10/20 = 0.5 hours


 and travels from B to A at an average 40km per hour.

10/40 = 0.25 hours

Total time = 0.75 hours
Total distance = 20 km

Speed = D/T = 20/0.75 = 26.67 km/h

30 = 20/ total time 
Let return time be x 

30 = 20/(0.5+x)
30(0.5+x) = 20

15+30x = 20
30x =5
x= 5/30 = 1/6 hour

Time B to A is 1/6 
Distance /time = speed

10/ (1/6) =60 km/h should be the return speed to get  average of total travel 
  
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