Average Velocity

We need to use a bit of algebra to do this, let's take the total distance to be, x km.

Now in the first case, the total distance traveled = $\frac{x}{2}$

Speed = 80 km/hr.

Time taken = ?

Hence, using, $time=\frac{distance}{speed}$ , we get time = $\displaystyle\frac{\frac{x}{2}}{80} = \frac{x}{160}$

Similarly in case two, $time=\displaystyle\frac{\frac{x}{2}}{40} = \frac{x}{80}$

Now, the average velocity is given by,

$\displaystyle \frac{total \quad distance}{time \quad taken}= \frac{x}{\frac{x}{160}+ \frac{x}{80}}$

[ because total time is time taken in case 1 plus case 2 ]

That is, $\displaystyle \frac{x}{\frac{3x}{160}}=\frac{160}{3}=\boxed{53.34}$

traveling 160km would take 3 hours 1 hour at 80km/h 2 hours at 40km/h 160/3= 53.3333333....