Question

I row against a stream flowing 1½ km an hour to a certain point and then turn back stopping 2km short of the place whence i originally started. If the whole time occupied in rowing be 2hrs 10mins and my inform speed in still water be 4½ km an hour find how far upstream I went.​

Answer 1

The man went upstream a distance of 5 km

Explanation:

Speed of the man in still water = 4.5 km/hr

Speed of the stream = 1.5 km/hr

Speed of the man upstream = 4.5 - 1.5 = 3 km/hr

Speed of the man downstream = 4.5 + 1.5 = 6 km/hr

If the man rows x km upstream then

Time taken = x/3 hour

Similarly time taken in travelling doownstrem a distance x - 2

= (x - 2)/6

Total time taken by the man = 2 hour 10 minute = 2 + 1/6 hours = 13/6 hours

Thus

x/3 + (x - 2)/6 = 13/6

or, 2x + x - 2 = 13

⇒ 3x = 15

⇒ x = 5

Therefore, the man went upstream a distance of 5 km

Hope this helps.