If a sailer sails 12 km distance within 5 hours against the flow of a river. If he sails 22 km distance in same time along the flow of the river. Then velocity of the river is _______

A boat goes from A to B in upstream and come back from B to A downstream taking a total time of 3.5 hours. If the speed of boat in still water is 7 km/hr and the speed of stream is 5 km/hr. Find the distance between A and B. 

A boat covers 48 km. upstream and 72 km. downstream in 12 hours, while it covers 72 km. upstream and 48 km. downstream is 13 hours. The speed of stream is -

A boat goes 15 km in an hour in still water, and takes thrice the time to cover the same distance upstream. The speed of the current (in km / hr) is –