Boats and Streams

The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is:

A boat is rowed down a river 40 km in 5 hr and up a river 21 km in 7 hr. Find the speed of the boat and the river.

A man can row 6 km/ hr in still water. If it takes him twice as long to row up, as to row down the river, then the rate of current in the stream is:

A boat takes 90 minutes less to travel 24 km downstream than to travel the same distance upstream. If the speed of the boat in still water is 12 km/h, the speed of the stream is:

A boat sails 15 km upstream in 5 hrs. How long will it take to cover the same distance downstream, if the speed of current is one-fourth the speed of the boat in still water 

A boat covers a certain distance downstream in 1 hour, while it comes back upstream in 1 1/2 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?  

A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:

A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:

A person can row with the stream at 8 km/hr and against the stream at 6 km/hr. The speed of the current is:

A motorboat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in 4 hrs and 30 mins. The speed of the stream is: