A person walks a distance of 40m towards west with a speed of 2m/s and 20m towards north with a speed of  4m/s. Then the average velocity for his journey.

Displacement along west  $S_1=40m$
Time taken  $t_1=\frac{40}{2}=20S$
Displacement along north  $S_2=20m$
Time taken  $t_2=\frac{20}{4}=5S$
$\therefore$ Displacement Vector  $\overline{S}=40\widehat{i}+20\widehat{j}$
$\therefore$ Total displacement  $S=\sqrt{S_1^2+S_2^2}$
                                 $\begin{array}{l}=\sqrt{{40}^2+{20}^2}\\ =\sqrt{1600+400}\\ =\sqrt{2000}=20\sqrt{5}\end{array}$
$\therefore$ Average velocity $\begin{array}{r}=\frac{\text{ Total displacement }}{\text{ Total time }}\end{array}$

                                  $\begin{array}{l}=\frac{20\sqrt{5}}{20+5}=\frac{20\sqrt{5}}{25}=\frac{4\sqrt{5}}{5}\\ =\frac{4}{\sqrt{5}}=\frac{4}{2.24}\\ =1.78\mathrm{m}/\mathrm{s}\end{array}$