1. An aeroplane left 50 minutes later than its schedule time and in order to reach the destination 1250km away, in time it had to increase its speed by 250 km/hr from its usual speed. Find is usual speed 2. An aeroplane takes 1 hour less for a journey of 1200km if its speed is increased by 100 km/hr from its usual speed of the plane. 3. A motorboat heads upstream a distance of 30 km on a river whose current is running at 5km/hr. The trip up and back takes 4 hours. Write a quadratic equation to find the speed of the boat. 4. A speedboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. What is the speed of the stream in km/hr?