Question

A man walks at 5kmph for 6hr and at 4km/h for 12hr. His average speed is

A. 4 1/3 km/h

B. 7 2/3 km/h

C. 9 ½ km/h

D. 8 km/h

Answer 1

The answer is
=5×6+4×12 / 18
=4 1/3
Therefore the correct option is A.



Hope it helps!!

Answer 2

The average speed of man is $\bold{4 \frac{1}{3}\ k m / h}$.

Average speed $=\frac{\text {Total Distance Travelled}}{\text {Total Time taken}}$.

We have taken the walking of the man into two cases.

In the case 1:  

The walking speed of man $S_{1}=5\ \mathrm{km} / \mathrm{hr}$

And the time taken for a certain distance in case 1 $T_{1}=6\ hours$

In the case 2:  

The walking speed of man $S_{2}=4\ \mathrm{km} / \mathrm{hr}$

And the time taken for a certain distance in case 2 $T_{2}=12\ hours$

As we know,

$\begin{array}{c}{\text {Distance}=\text {speed} \times \text { time }} \\ {D_{1}=5 \times 6=30\ \mathrm{km}} \\ {D_{2}=4 \times 12=48\ \mathrm{km}}\end{array}$

Therefore,

$Average\ speed=\frac{30+48}{6+12}$

$\begin{array}{c}{=\frac{78}{18}} \\ \\ {=\frac{13}{3}} \\ \\{=4 \frac{1}{3}\ k m / h r}\end{array}$