A person rowing at the rate of 5 km/hr in still water, takes thrice as much time in going 40 km upstream as in going 40 km downstream.Find the speed of the stream.

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Solution

Let the speed of ht stream be v km/h
The speed of a person rowing in still water = 5km/h
The speed of a person rowing in downstream = (5 + v)km/h
And the speed of a person has rowing in upstream = ( 5 – v ) km/h
Now, the person taken time to cover 40 km downstream
$t subscript 1 equals fraction numerator 40 over denominator 5 plus v end fraction$
to cover 40 km upstream
$t subscript 2 equals fraction numerator 40 over denominator 5 minus v end fraction$

Now it is given,

$fraction numerator 40 over denominator 5 minus v end fraction equals 3 left parenthesis space fraction numerator 40 over denominator 5 plus v end fraction right parenthesis 5 plus v equals 15 minus 3 v 4 v equals 10 v equals 2.5$

Hence the speed of stream is 2.5 Km/hr

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