Question

a boat tales 3 hrs to go 45 km downstream and it return back in 9 hours . Find the speed of the stream and that of the boat in still water​

Answer 1

Answer:

Let’s assume the speed of the boat in still water be x km/hr

And the speed of the stream =y km/hr

So, the speed of the boat in downstream =(x+y) km/hr

The speed of the boat in upstream =(x−y) km/hr

We know that,

Distance=Speed×Time

Now, according to the given conditions in the problem, we have

40=(x+y)×2

⇒x+y=20 … (i)

And,

40=(x−y)×4

⇒x−y=10 … (ii)

Adding (i) and (ii), we have

2x=30

⇒x=15

On substituting the value of x in equation (i), we have

15+y=20

⇒y=20−15

⇒y=5

Therefore,

Speed of the boat in still water =15 km/hr and

Speed of the stream =5 km/hr.

Answer 2

Explanation:

Let’s assume the speed of the boat in still water be x km/hr

And the speed of the stream =y km/hr

So, the speed of the boat in downstream =(x+y) km/hr

The speed of the boat in upstream =(x−y) km/hr

We know that,

Distance=Speed×Time

Now, according to the given conditions in the problem, we have

40=(x+y)×2

⇒x+y=20 … (i)

And,

40=(x−y)×4

⇒x−y=10 … (ii)

Adding (i) and (ii), we have

2x=30

⇒x=15

On substituting the value of x in equation (i), we have

15+y=20

⇒y=20−15

⇒y=5

Therefore,

Speed of the boat in still water =15 km/hr and

Speed of the stream =5 km/hrs.