Answers

2014-09-05T09:45:36+05:30
Average speed of first 
distance = 20 km 
speed = 40 km/h 
time taken  = 20/40 = 1/2 hrs 
2nd time average 
distance = 20 km 
speed = 60 km/h 
time taken by the car is  = 20/60 = 1/3 hrs 

total time taken = t1+t2 = 1/2 +1/3 = 5/6 hrs 

Average speed of the car is = (20+20)/(5/6) 
= 48 km/h >===========================< ANSWER
3 3 3
we can use the formula of 2xy / x + y , where x = 40 & y = 60, therfore 2 * 40 * 60 / 40 + 60 = 48
welcme friend
we can use this farmula also ( average speed=tota distance / total time )
2014-09-05T09:53:27+05:30
Distance = 20 km 
Speed = 40 km/hr
Time, t1 = 20/40 = 1/2 hrs 

Speed = 60 km/h 

Time, t2 = 20/60 = 1/3 hrs 

Total time = t1 + t2 = 1/2 + 1/3 = 5/6 hrs 

Average speed = (20+20)/(5/6) 
= 48 km/hr
2 5 2
if it was useful please mark as best