Question

An aeroplane take 1 hour less for a journey of 1200 km if its speed is increased by 100 km/hr from its usual speed. Find its usual speed.

Answer 1

Let the usual speed of aero plane be. Then,

Increased speed of the aero plane

Time taken by the aero plane under usual speed to cover

Time taken by the aero plane under increased speed to cover

Therefore,

So, either

Or

But, the speed of the aero plane can never be negative.

Hence, the usual speed of train is