Question

A man can row a boat downstream 20 km in 2 hours and upstream 4 km in 2 hours. Find his speed of rowing in still water. Also find the speed of the stream.​

Answer 1

Answer:

Let, speed of man in still water be x km/hr

and speed of current be y km/hr

Then speed downstream =(x+y) km/hr

speed upstream =(x−y) km/hr

we know, Time=

Speed

Distance

Then

x+y

20

=2 and

x−y

4

=2

⇒x+y=10 ...(1)

& x−y=2 ...(2)

adding both we get, 2x=12⇒x=6

Thus using (1) y=10−6=4

Hence the speed of man in still water is 6 km/hr and the speed of the current is 4 km/hr.

Step-by-step explanation:

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Answer 2

Answer:

Speed of a boat in still water = 6 km/hr

and speed of the stream = 4km/hr.

Step-by-step explanation:

Let the speed of the boat in still water be $x$ km/hr and speed of the stream be $y$ km/hr.

∴ Relative Speed of boat in upstream = $(x-y)$ km/he and Relative Speed in downstream = $(x+y)$ km/hr.

According to question,

$\frac{20}{x+y} = 2\\\implies x+y = 10\: \: \: \: \: ....(i)\\and \: \frac{4}{x-y} = 2\\\implies x-y = 2 \: \: \: \: ....(ii)$

On adding eq. (i) and (ii), we get

$2x = 12$

$\implies x = 6$

Putting the value of $x$ in eq. (i),

$6+y = 10$

$\implies y = 10-6 = 4$

Speed of a boat in still water = 6 km/hr

and speed of the stream = 4km/hr.