Answer :

Given:

speed from a to b=30 km/h
speed from b to a=20 km/h

Formula used :

1.average speed 

let distance from a to b be "D"

as we know 

2. speed of an object 
where 
s is the speed of the object
d is the distance traveled by the object
t is the time taken by the object to travel distance D

putting the value of s a to b in equation 2

D=30 × T1                                     (3)


putting the value of s b to a in equation 2

D =20 × T2                                      (4)

using equation 3 and 4, we get
 
30 × T= 20 × T2

T= 1.5 × T1

The total distance traveled by the body is D+D =2 × D 

The total time taken by the body is T1 + T2= T+1.5×T1= 2.5 × T1

putting the value in equation 1 , we get


The average speed of the object is 24 km/h  

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