Question

a car travels from a to b at a speed of 20km/hr and returns at a speed of 3okm/hr what is the average speed

Answer 1

Hii frnd..

the speed average is

Total average speed is simply = Total distance/Total time 
Lets say, 
D = distance travelled by the car in EACH direction 
t1 = time spent on onward trip 
t2 = time spent on return trip 
Thus, the total distance travelled by the car = D+D= 2D 
And, by the formula, Speed = Distance/Time 
S1 = D/t1 => t1 = D/S1 
S2 = D/t2 => t2 = D/S2 
Total average speed = Total Distance/Total time = 2D/(t1+t2) = 2D/(D/S1+D/S2) = 2S1*S2/(S1+S2) 

Remember this general formula for a total average speed problems: 
Total average speed = 2S1*S2/(S1+S2) 


So in the question S1 = 20km/hr 


                         &S2 = 30km/hr


So av. speed = 2 x 20 x 30/20+30


                   = 24km/hr




24km / hr