Q. A boat running downstream covers a distance of 20 km in 2 hrs while it covers the same distance upstream in 5 hrs. Then speed of the both in still water is:
Answer:
7 km/hr
Notes: Let the speed of boat in still water be x kmph and that of stream be y kmph.
$ \therefore \frac{20}{x+y} = 2$
$ => x+y = 10$ …….(1)
$ \frac{20}{x-y} = 5$
$ => x-y = 4$…………(2)
On adding, 2x = 14 kmph = 7 kmph
Hence option [C] is the right answer.