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Home » A person rowing at the rate of 5km/h in still water, takes thrice as much time in going 40 km upstream as in going 40km downstream. Find the speed of the stream.
A person rowing at the rate of 5km/h in still water, takes thrice as much time in going 40 km upstream as in going 40km downstream. Find the speed of the stream.
CBSE | Class 10 | Exercise 3.10 | Maths | Pair of Linear Equations In Two Variables | RD Sharma
A person rowing at the rate of 5km/h in still water, takes thrice as much time in going 40 km upstream as in going 40km downstream. Find the speed of the stream.

Let’s assume C to be the speed of the stream.

So, we know that

Speed of boat in downstream =(5+C) and,

Speed of boat in upstream =(5-C)

It is given that,

The distance in one way is 40km.

And,

Time taken during upstream =3C time taken during the downstream

Expressing it by equations, we have

40/\left( 5-C \right)=3\times 40/\left( 5+C \right) [∵ time = distance/ speed]

BD cross multiplication, we get

(5+C)=3(5-C)

⇒ 5+C=3(5-C)

⇒ C+3C=15-5

⇒ C=10/4=2.5

Therefore, the speed of the stream is 2.5km/hr.

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