Hi Folks,

The purpose of this post is to clarify the concept of average speed,

which is not equal to the average of two speeds.Basic Formula : Distance=Speed*Time

D=T*S

Average Speed= Total Distance/Total time taken

Say, a body covers distance D in two parts. D=d1+d2

d1 distance at an average speed s1

and

d2 distance at an average speed s2

(using T=D/S)

We know that Average Speed = [d1+d2][/t1+t2]

Therefore we need to calculate the time taken for each fraction of journey :

time taken to cover d1,say t1 = d1/s1

time taken to cover d1,say t2 = d2/s2

Average Speed= [d1+d2][/d1/s1+d2/s2]

Simplifying :

Average Speed = [d1+d2]*s1*s1/ (s1*d2+s2*d1)

Specific Case :

For round Trips : d1=d2=d

the formula reduces to ::

Average Speed = (2d*s1*s2)/(s1*d+s2*d)

= 2(s1*s2)/(s1+s2) * for round trips, if we are given the speeds, we do not need the total distance to calculate the Avg Speed.

**If anyone can, please do post the questions on this topic.

Hope that Helps!!

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