Question

A boat makes a return journey from point A to point B and back in 5 hours 36 minutes. One way it travels with the stream and on the return it travels against the stream. If the speed of the stream increases by 2 km/hr, the return journey takes 9 hours 20 minutes. What is the speed of the boat in still water? (The distance between A and B is 16 km.)

Answer 1

The speed of the boat in still water is 7km /hr

Given :

• Return journey of the boat from point A to point B takes 5hours 36mins
• Speed of the stream increases by 2km/hr
• The return journey takes 9hours 20mins
• distance between A and B is 16km

To find :

The speed of boat in still water

Solution :

Let x be speed of u / s and y be the speed of d / s.

According to the problem,

(16/x) + (16/y) = (28/5)

and 16/(y+2) + 16/(x-2) = 28/3

Equating these two equations, we get

x = 4km/hr

and y = 10km/hr

∴ Speed of boat in still water = (4+10) / 2 = 7km/hr.

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Answer 2

Given :

A boat makes a return journey from point $A$ to point $B$ and back in $5$ hours $36$ minutes. One way it travels with the stream and on the return it travels against the stream.

The speed of the stream increases by $2 km/hr$, the return journey takes $9$ hours $20$ minutes.

The distance between $A$ and $B$ is $16km$

We have to find the speed of boat in still water.

Let $x$ be speed of upstream and $y$ be the speed of down stream.

According to the problem,

$(16/x) + (16/y) = (28/5)$

$16/(y+2) + 16/(x-2) = 28/3$

Now, solving these two equations, we get

$x = 4km/hr$

And, $y = 10km/hr$

The speed of boat in still water $=\frac{Up stream speed+Down stream speed}{2}$

$= \frac{2+10}{2}$

$=\frac{14}{2}$

$=7 km/hr$

Therefore, the speed of the boat in still water is $7 km/hr$.