Kartik walks from point $A$ to $B$ with $50\text{ km/hr}$ speed and returns $B$ to $A$ with speed of $30\text{ km/hr}$. Find his average speed.

When an equal distance is covered at two different speeds, say $x$ and $y$, the average speed for the entire journey is given by the harmonic mean formula:
$$\text{Average Speed}=\frac{2xy}{x+y}$$

Given:

* Forward speed ($x$) $=50\text{ km/hr}$
* Return speed ($y$) $=30\text{ km/hr}$

$$\text{Average Speed}=\frac{2\times 50\times 30}{50+30}$$

$$\text{Average Speed}=\frac{3000}{80}=\frac{300}{8}=37.5\text{ km/hr}$$