Question

A man goes uphill with an average speed of 35 km/hr and comes down with an average speed of 45 km/hr. The distance travelled in both the cases being the same, the average speed for the entire journey is:

Answer 1

Given:

A man goes uphill with an average speed of 35 km/h and comes down with an average speed of 45 km/h.

To Find:

The average speed for the entire journey.

Solution:

Since here, man goes uphill with an average speed of 35 km/h and comes down with an average speed of 45 km/h and also, distance travelled in both the cases are same.

let,

$S1= 35km/h$ = average speed of man when he goes uphill and

$S2=45 km/h$ = average speed of man when he comes from uphill.

also, let, $d1=d2=d$, d1 and d2 are the distances travelled by when he goes and comes from hill respectively.

In this case, Average speed = S

$S= \dfrac{2(S1)(S2)}{S1+S2}$    

here,

$S=\dfrac{2(35)(45)}{35+45}\\\\ =\dfrac{3150}{80}\\\\=\dfrac{315}{8}$

Hence, Average speed for the entire journey is 315/8 km/h .