A bus travels 720 km. in 20 hours. Calculate its average speed in metre/second.
A racing car going at an average speed of 108 km./hr. takes 15 minutes to complete a lap on a racing track. By how much should it increase its speed (in km./hr.) to complete the lap in 12 minutes ?
Train A takes 45 minutes more than B to travel a distance of 450 km. Due to engine trouble speed of train B falls by a quarter, so it takes 30 minutes more than Train A to complete the same journey. What is the speed of Train A (in km./hr.) ?