Question

A man rows to a place 60 km distance and .He finds that he can row 5 km with the stream in the same time as 4 km against the stream .What is the rate of the stream ?

Answer 1

The question is incomplete. Here is the complete question:

A man rows to a place of 60 km distant and back in 13 hour 30 minutes. He finds that he can row 5 km with the stream in the same time as he can row 4 km against the stream. FInd the rate of stream.

a) 1 km/hr

b) 1/2 km/hr

c) 3/2 km/hr

d) 8 km/hr

Answer:

Assume that he moves 5 km downstream in t hours.

Then, speed downstream = distance/time= 5/t km/hr

speed upstream = 4/t km/hr

He rows to a place 60 km distant and come back in 13.5 hours (13 hour 30 minute) \

t = 0.5

Speed downstream = 5/0.5 = 10 km/hr

Speed upstream = 4/0.5 = 8 km/hr

Speed in still water = (Speed downstream - Speed upstream)/2 = (10-8)/2 = 1 km/hr

If there is any confusion please leave a comment below.

Answer 2

From the data given,

Let us assume that the man moves 5km downstream in t hours.

Then, Speed = Distance/Time

Speed downstream = 5/t.

Now let us assume that the man moves upstream for 4km in t hours.

Speed upstream = 4/t.

The man rows to a place at a distance of 60 km and comes back in 13.5 hours (13 hours and 30 minutes)  

The time taken, t = 60/(5/t)+60/(4/t)

Therefore, t = 0.5 Hours.

Speed downstream = 5/0.5 = 10 km/hr

Speed upstream = 4/0.5 = 8 km/hr

Speed in still water = ( Speed downstream - Speed upstream ) / 2

= (10-8) / 2

= 1 km/hr