Question

# A car travels from A  and B at a speed of $$20km/hr$$ and returns at a speed of $$30km/hr$$. The average speed of the car for the whole journey is

A
25km/hr
B
24km/hr
C
50km/hr
D
5km/hr

Solution

## The correct option is B $$24km/hr$$Lets consider $$X=$$ distance between A and B.A car travels from A to B with speed of $$20km/h$$  at time,$$t_1=\dfrac{x}{20}hr$$A car return from B to A with speed $$30km/h$$ at time $$t_2$$$$t_2=\dfrac{x}{30}hr$$Average speed, $$v_{avg}=\dfrac{Total \, distance}{Total \, time}$$$$v_{avg}=\dfrac{2x}{t_1+t_2}=\dfrac{2x}{\dfrac{x}{20}+\dfrac{x}{30}}$$$$v_{avg}=\dfrac{2x}{x/12}$$$$v_{avg}=2\times 12$$$$v_{avg}=24km/h$$The correct option is B.Physics

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