The distance between two towns is covered in 7 hours at a speed of 50 km/h. By how much should the speed (in km/h) be increased so that 2 hours of travelling time will be saved?

20

Distance = Speed × Time

Distance = 50 × 7 = 350 km

To cover distance in 2 hour less . i.e. 5 hours

Speed = $\frac{350}{5}$ = 70  km/h

Increment in speed = 70 - 50 =  20 km/h