A man goes from A to B at 40 km/ hr speed and returns from B to A at 60 km/ hr speed . Find average speed??

Question

I’m getting  confused 

Answer 1

Distance = (Rate)(Time)  So, Time = Distance / Rate

 

Let D = one-way distance.  Then: 

 

 Time it takes to go from A to B = D/40

 Time it takes to go from B to A = D/60

 

Average speed = (Total Distance) / (Total time)

 

                      =  2D / [D/40 + D/60]

 

                      = 2D/[D/24] = 2D(24/D) = 48 km/hr

 

Answer 2

Hello Lakshmi,

The question being asked is usually confused with the phrase, 'Find the average (of the) speed(s).'  What they are looking for in the problem is the average speed of the entire trip.

 

The formula for this would be:

r_avg = (2*r₁*r₂)/(r₁ + r₂)

 

 

I hope the above helps.  If the teacher did not provide the formula, or if it is not in the text, just let me know, and I will show you how to derive it.

 

Thank you for the question.

Michael E.