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 ?
Answers
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.
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