Question

A scoorterist goes to a one place at the sepeed of 20 km/hr and returns at the speed of 30 km/hr. Find avg speed of entire jurney

Answer 1

As we know that,

Average Speed = Total Distance/Total time.

Since, Distance is not given so

Let, the Distance = x

=> Time for going = x/20

=> Time for coming = x/30

=> Total Time = x/20 + x/30 = 3x + 2x/60

=> Total time = 5x/60

=> Total time = x/12

As we also know that, in this trip questions the Distance becomes twice.

So,

=> Distance = 2x

=> Average Speed = Distance/Time

$=> S_{avg} = \dfrac{2x}{\frac{x}{12} }$

$=> S_{avg} = 2x \times \dfrac{12}{x}$

$=> S_{avg} = (2 \times 12) Km{h}^{-1}$

$=> S_{avg} = 24 Km{h}^{-1}$

Answer 2

Since we don't know the distance we will call this  D

The time for the out trip is  D/ 20

and the return trip will take D /30  (in hours)

The total time will be  t = D/20 +  D/30 =  (3 D/60 +  2D/60) = D/12

for a distance of  2D.

Average speed = 2D / (D/12) = 2D *12/D

= 24km/hr

Hope this helps you.