# Question #ed6fb

$\frac{170}{7}$ km/h.

#### Explanation:

The Average velocity which is needed to qualify for the race : 200 km/h.

Let the distance for each lap be $x$ km.
The Total distance is = $4 x$ km.

then total time taken to finish the race at average velocity 200km/h is = $\frac{4 x}{200}$ h.
If average velocity decraeses to 170 km/h,
then Total time taken to cover two laps = $\frac{2 x}{170}$ h.

Remaining time to finish and qualify for the race is = $\left\{\frac{4 x}{200} - \frac{2 x}{170}\right\} = \frac{\left(4 x \cdot 170\right) - \left(2 x \cdot 200\right)}{3400} = \frac{280 x}{3400} = \frac{7 x}{85}$ h.

So the average velocity to complete and qualify for the race is =

$\frac{2 x \cdot 85}{7 x} = \frac{170}{7}$ km/h.