Question

A man want uphill with a speed of 20 km.p.h. and came downhill with a speed of 30 km p.h. the average speed for his journey was

Answer 1

i think the average speed is 25mph 

Answer 2

The average speed of his journey is 24 km/hr

Given:

Speed of the man while going uphill (a) = 20 kmph

Speed of the man while coming downhill (b) = 30 kmph

To find:

The average speed of his journey

Solution:

a = 20 km/hr

Since going up a hill needs more energy  

b = 30 km/hr

And, since going down a hill needs lesser energy.

Thus, both the uphill and the downhill speeds are different and not same.  

So new need to find the average speed or the mean speed of the man.

∴ Average speed of the man $\begin{aligned} n &=\frac{2 a b}{a+b} \\ &=\frac{2 \times 20 \times 30}{20+30} \\ &=\frac{1200}{50} \\ &=24 \mathrm{kmph} \end{aligned}$

The average speed of his journey is 24 km/hr