Question

At his usual rowing rate, Rahul can travel 12 miles downstream in a certain river in 6 hours less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his 24 mile round trip, the downstream 12 miles would then take only one hour less than the upstream 12 miles. What is the speed of the current in miles per hour? 

(a) \(1\frac13\)

(b) \(1\frac23\)

(c) \(2\frac13\)

(d) \(2\frac23\)

Answer 1

(d)  \(2\frac23\) mph

Let the speed of the boat in still water be x mph and speed of the current be y mph. Then, 

Speed upstream = (x – y) mph and stream downstream = (x + y) mph

∴ Speed of the current = \(\frac83\) mph = \(2\frac23\) mph.